Context

class moderngl.Context

Class exposing OpenGL features.

ModernGL objects can be created from this class.

Create

moderngl.create_context(require: Optional[int] = None, standalone: bool = False, share: bool = False, **settings: Dict[str, Any]) Context

Create a ModernGL context by loading OpenGL functions from an existing OpenGL context. An OpenGL context must exists.

Example:

# Accept the current context version
ctx = moderngl.create_context()

# Require at least OpenGL 4.3
ctx = moderngl.create_context(require=430)

# Create a headless context requiring OpenGL 4.3
ctx = moderngl.create_context(require=430, standalone=True)
Keyword Arguments
  • require (int) – OpenGL version code (default: 330)

  • standalone (bool) – Headless flag

  • share (bool) – Attempt to create a shared context

  • **settings – Other backend specific settings

Returns

Context object

moderngl.create_standalone_context(require: Optional[int] = None, share: bool = False, **settings: Dict[str, Any]) Context

Create a standalone/headless ModernGL context.

The preferred way of making a context is through moderngl.create_context().

Example:

# Create a context with highest possible supported version
ctx = moderngl.create_context()

# Require at least OpenGL 4.3
ctx = moderngl.create_context(require=430)
Keyword Arguments
  • require (int) – OpenGL version code.

  • share (bool) – Attempt to create a shared context

  • settings – keyword config values for the context backend

Returns

Context object

ModernGL Objects

Context.program(*, vertex_shader: str, fragment_shader: Optional[str] = None, geometry_shader: Optional[str] = None, tess_control_shader: Optional[str] = None, tess_evaluation_shader: Optional[str] = None, varyings: Tuple[str, ...] = (), fragment_outputs: Optional[Dict[str, int]] = None, varyings_capture_mode: str = 'interleaved') Program

Create a Program object.

The varyings are only used when a transform program is created to specify the names of the output varyings to capture in the output buffer.

fragment_outputs can be used to programmatically map named fragment shader outputs to a framebuffer attachment numbers. This can also be done by using layout(location=N) in the fragment shader.

Parameters
  • vertex_shader (str) – The vertex shader source.

  • fragment_shader (str) – The fragment shader source.

  • geometry_shader (str) – The geometry shader source.

  • tess_control_shader (str) – The tessellation control shader source.

  • tess_evaluation_shader (str) – The tessellation evaluation shader source.

  • varyings (list) – A list of varyings.

  • fragment_outputs (dict) – A dictionary of fragment outputs.

Returns

Program object

Context.simple_vertex_array(program: Program, buffer: Buffer, *attributes: Union[List[str], Tuple[str, ...]], index_buffer: Optional[Buffer] = None, index_element_size: int = 4, mode: Optional[int] = None) VertexArray

Create a VertexArray object.

Warning

This method is deprecated and may be removed in the future. Use Context.vertex_array() instead. It also supports the argument format this method describes.

Parameters
  • program (Program) – The program used when rendering.

  • buffer (Buffer) – The buffer.

  • attributes (list) – A list of attribute names.

Keyword Arguments
  • index_element_size (int) – byte size of each index element, 1, 2 or 4.

  • index_buffer (Buffer) – An index buffer.

  • mode (int) – The default draw mode (for example: TRIANGLES)

Returns

VertexArray object

Context.vertex_array(*args, **kwargs) VertexArray

Create a VertexArray object.

The vertex array describes how buffers are read by a shader program. We need to supply buffer formats and attributes names. The attribute names are defined by the user in the glsl code and can be anything.

Examples:

# Empty vertext array (no attribute input)
vao = ctx.vertex_array(program)

# Simple version with a single buffer
vao = ctx.vertex_array(program, buffer, "in_position", "in_normal")
vao = ctx.vertex_array(program, buffer, "in_position", "in_normal", index_buffer=ibo)

# Multiple buffers
vao = ctx.vertex_array(program, [
    (buffer1, '3f', 'in_position'),
    (buffer2, '3f', 'in_normal'),
])
vao = ctx.vertex_array(program, [
        (buffer1, '3f', 'in_position'),
        (buffer2, '3f', 'in_normal'),
    ],
    index_buffer=ibo,
    index_element_size=2,  # 16 bit / 'u2' index buffer
)

This method also supports arguments for Context.simple_vertex_array().

Parameters
  • program (Program) – The program used when rendering

  • content (list) – A list of (buffer, format, attributes). See Buffer Format.

Keyword Arguments
  • index_buffer (Buffer) – An index buffer (optional)

  • index_element_size (int) – byte size of each index element, 1, 2 or 4.

  • skip_errors (bool) – Ignore errors during creation

  • mode (int) – The default draw mode (for example: TRIANGLES)

Returns

VertexArray object

Context.buffer(data: Optional[Any] = None, *, reserve: int = 0, dynamic: bool = False) Buffer

Create a Buffer object.

Parameters

data (bytes) – Content of the new buffer.

Keyword Arguments
  • reserve (int) – The number of bytes to reserve.

  • dynamic (bool) – Treat buffer as dynamic.

Returns

Buffer object

Context.texture(size: Tuple[int, int], components: int, data: Optional[Any] = None, *, samples: int = 0, alignment: int = 1, dtype: str = 'f1', internal_format: Optional[int] = None) Texture

Create a Texture object.

Warning

Do not play with internal_format unless you know exactly you are doing. This is an override to support sRGB and compressed textures if needed.

Parameters
  • size (tuple) – The width and height of the texture.

  • components (int) – The number of components 1, 2, 3 or 4.

  • data (bytes) – Content of the texture.

Keyword Arguments
  • samples (int) – The number of samples. Value 0 means no multisample format.

  • alignment (int) – The byte alignment 1, 2, 4 or 8.

  • dtype (str) – Data type.

  • internal_format (int) – Override the internalformat of the texture (IF needed)

Returns

Texture object

Context.depth_texture(size: Tuple[int, int], data: Optional[Any] = None, *, samples: int = 0, alignment: int = 4) Texture

Create a Texture object.

Parameters
  • size (tuple) – The width and height of the texture.

  • data (bytes) – Content of the texture.

Keyword Arguments
  • samples (int) – The number of samples. Value 0 means no multisample format.

  • alignment (int) – The byte alignment 1, 2, 4 or 8.

Returns

Texture object

Context.texture3d(size: Tuple[int, int, int], components: int, data: Optional[Any] = None, *, alignment: int = 1, dtype: str = 'f1') Texture3D

Create a Texture3D object.

Parameters
  • size (tuple) – The width, height and depth of the texture.

  • components (int) – The number of components 1, 2, 3 or 4.

  • data (bytes) – Content of the texture.

Keyword Arguments
  • alignment (int) – The byte alignment 1, 2, 4 or 8.

  • dtype (str) – Data type.

Returns

Texture3D object

Context.texture_array(size: Tuple[int, int, int], components: int, data: Optional[Any] = None, *, alignment: int = 1, dtype: str = 'f1') TextureArray

Create a TextureArray object.

Parameters
  • size (tuple) – The (width, height, layers) of the texture.

  • components (int) – The number of components 1, 2, 3 or 4.

  • data (bytes) – Content of the texture. The size must be (width, height * layers) so each layer is stacked vertically.

Keyword Arguments
  • alignment (int) – The byte alignment 1, 2, 4 or 8.

  • dtype (str) – Data type.

Returns

Texture3D object

Context.texture_cube(size: Tuple[int, int], components: int, data: Optional[Any] = None, *, alignment: int = 1, dtype: str = 'f1', internal_format: Optional[int] = None) TextureCube

Create a TextureCube object.

Note that the width and height of the cubemap must be the same unless you are using a non-standard extension.

Parameters
  • size (tuple) – The width, height of the texture. Each side of the cube will have this size.

  • components (int) – The number of components 1, 2, 3 or 4.

  • data (bytes) – Content of the texture. The data should be have the following ordering: positive_x, negative_x, positive_y, negative_y, positive_z, negative_z

Keyword Arguments
  • alignment (int) – The byte alignment 1, 2, 4 or 8.

  • dtype (str) – Data type.

  • internal_format (int) – Override the internalformat of the texture (IF needed)

Returns

TextureCube object

Context.external_texture(glo: int, size: Tuple[int, int], components: int, samples: int, dtype: str) Texture

Create a Texture object from an existing OpenGL texture object.

Parameters
  • glo (int) – External OpenGL texture object.

  • size (tuple) – The width and height of the texture.

  • components (int) – The number of components 1, 2, 3 or 4.

  • samples (int) – The number of samples. Value 0 means no multisample format.

  • dtype (str) – Data type.

Context.simple_framebuffer(size: Tuple[int, int], components: int = 4, *, samples: int = 0, dtype: str = 'f1') Framebuffer

Creates a Framebuffer with a single color attachment and depth buffer using moderngl.Renderbuffer attachments.

Parameters
  • size (tuple) – The width and height of the renderbuffer.

  • components (int) – The number of components 1, 2, 3 or 4.

Keyword Arguments
  • samples (int) – The number of samples. Value 0 means no multisample format.

  • dtype (str) – Data type.

Returns

Framebuffer object

Context.framebuffer(color_attachments: Any = (), depth_attachment: Optional[Union[Texture, Renderbuffer]] = None) Framebuffer

A Framebuffer is a collection of buffers that can be used as the destination for rendering. The buffers for Framebuffer objects reference images from either Textures or Renderbuffers.

Parameters
Returns

Framebuffer object

Context.renderbuffer(size: Tuple[int, int], components: int = 4, *, samples: int = 0, dtype: str = 'f1') Renderbuffer

Renderbuffer objects are OpenGL objects that contain images. They are created and used specifically with Framebuffer objects.

Parameters
  • size (tuple) – The width and height of the renderbuffer.

  • components (int) – The number of components 1, 2, 3 or 4.

Keyword Arguments
  • samples (int) – The number of samples. Value 0 means no multisample format.

  • dtype (str) – Data type.

Returns

Renderbuffer object

Context.depth_renderbuffer(size: Tuple[int, int], *, samples: int = 0) Renderbuffer

Renderbuffer objects are OpenGL objects that contain images. They are created and used specifically with Framebuffer objects.

Parameters

size (tuple) – The width and height of the renderbuffer.

Keyword Arguments

samples (int) – The number of samples. Value 0 means no multisample format.

Returns

Renderbuffer object

Context.scope(framebuffer: Optional[Framebuffer] = None, enable_only: Optional[int] = None, *, textures: Tuple[Tuple[Texture, int], ...] = (), uniform_buffers: Tuple[Tuple[Buffer, int], ...] = (), storage_buffers: Tuple[Tuple[Buffer, int], ...] = (), samplers: Tuple[Tuple[Sampler, int], ...] = (), enable: Optional[int] = None) Scope

Create a Scope object.

Parameters
  • framebuffer (Framebuffer) – The framebuffer to use when entering.

  • enable_only (int) – The enable_only flags to set when entering.

Keyword Arguments
  • textures (tuple) – List of (texture, binding) tuples.

  • uniform_buffers (tuple) – Tuple of (buffer, binding) tuples.

  • storage_buffers (tuple) – Tuple of (buffer, binding) tuples.

  • samplers (tuple) – Tuple of sampler bindings

  • enable (int) – Flags to enable for this vao such as depth testing and blending

Context.query(*, samples: bool = False, any_samples: bool = False, time: bool = False, primitives: bool = False) Query

Create a Query object.

Keyword Arguments
  • samples (bool) – Query GL_SAMPLES_PASSED or not.

  • any_samples (bool) – Query GL_ANY_SAMPLES_PASSED or not.

  • time (bool) – Query GL_TIME_ELAPSED or not.

  • primitives (bool) – Query GL_PRIMITIVES_GENERATED or not.

Context.compute_shader(source: str) ComputeShader

A ComputeShader is a Shader Stage that is used entirely for computing arbitrary information. While it can do rendering, it is generally used for tasks not directly related to drawing.

Parameters

source (str) – The source of the compute shader.

Returns

ComputeShader object

Context.sampler(repeat_x: bool = True, repeat_y: bool = True, repeat_z: bool = True, filter: Optional[Tuple[int, int]] = None, anisotropy: float = 1.0, compare_func: str = '?', border_color: Optional[Tuple[float, float, float, float]] = None, min_lod: float = -1000.0, max_lod: float = 1000.0, texture: Optional[Texture] = None) Sampler

Create a Sampler object.

Keyword Arguments
  • repeat_x (bool) – Repeat texture on x

  • repeat_y (bool) – Repeat texture on y

  • repeat_z (bool) – Repeat texture on z

  • filter (tuple) – The min and max filter

  • anisotropy (float) – Number of samples for anisotropic filtering. Any value greater than 1.0 counts as a use of anisotropic filtering

  • compare_func – Compare function for depth textures

  • border_color (tuple) – The (r, g, b, a) color for the texture border. When this value is set the repeat_ values are overridden setting the texture wrap to return the border color when outside [0, 1] range.

  • min_lod (float) – Minimum level-of-detail parameter (Default -1000.0). This floating-point value limits the selection of highest resolution mipmap (lowest mipmap level)

  • max_lod (float) – Minimum level-of-detail parameter (Default 1000.0). This floating-point value limits the selection of the lowest resolution mipmap (highest mipmap level)

  • texture (Texture) – The texture for this sampler

Context.clear_samplers(start: int = 0, end: int = -1) None

Unbinds samplers from texture units.

Sampler bindings do clear automatically between every frame, but lingering samplers can still be a source of weird bugs during the frame rendering. This methods provides a fairly brute force and efficient way to ensure texture units are clear.

Keyword Arguments
  • start (int) – The texture unit index to start the clearing samplers

  • stop (int) – The texture unit index to stop clearing samplers

Example:

# Clear texture unit 0, 1, 2, 3, 4
ctx.clear_samplers(start=0, end=5)

# Clear texture unit 4, 5, 6, 7
ctx.clear_samplers(start=4, end=8)
Context.release() None

Release the ModernGL context.

If the context is not standalone the standard backends in glcontext will not do anything because the context was not created by moderngl.

Standalone contexts can normally be released.

Methods

Context.clear(red: float = 0.0, green: float = 0.0, blue: float = 0.0, alpha: float = 0.0, depth: float = 1.0, *, viewport: Optional[Union[Tuple[int, int], Tuple[int, int, int, int]]] = None, color: Optional[Tuple[float, float, float, float]] = None) None

Clear the bound framebuffer.

If a viewport passed in, a scissor test will be used to clear the given viewport. This viewport take prescense over the framebuffers scissor. Clearing can still be done with scissor if no viewport is passed in.

This method also respects the color_mask and depth_mask. It can for example be used to only clear the depth or color buffer or specific components in the color buffer.

If the viewport is a 2-tuple it will clear the (0, 0, width, height) where (width, height) is the 2-tuple.

If the viewport is a 4-tuple it will clear the given viewport.

Parameters
  • red (float) – color component.

  • green (float) – color component.

  • blue (float) – color component.

  • alpha (float) – alpha component.

  • depth (float) – depth value.

Keyword Arguments
  • viewport (tuple) – The viewport.

  • color (tuple) – Optional rgba color tuple

Context.enable_only(flags: int) None

Clears all existing flags applying new ones.

Note that the enum values defined in moderngl are not the same as the ones in opengl. These are defined as bit flags so we can logical or them together.

Available flags:

  • moderngl.NOTHING

  • moderngl.BLEND

  • moderngl.DEPTH_TEST

  • moderngl.CULL_FACE

  • moderngl.RASTERIZER_DISCARD

  • moderngl.PROGRAM_POINT_SIZE

Examples:

# Disable all flags
ctx.enable_only(moderngl.NOTHING)

# Ensure only depth testing and face culling is enabled
ctx.enable_only(moderngl.DEPTH_TEST | moderngl.CULL_FACE)
Parameters

flags (EnableFlag) – The flags to enable

Context.enable(flags: int) None

Enable flags.

Note that the enum values defined in moderngl are not the same as the ones in opengl. These are defined as bit flags so we can logical or them together.

For valid flags, please see enable_only().

Examples:

# Enable a single flag
ctx.enable(moderngl.DEPTH_TEST)

# Enable multiple flags
ctx.enable(moderngl.DEPTH_TEST | moderngl.CULL_FACE | moderngl.BLEND)
Parameters

flag (int) – The flags to enable.

Context.disable(flags: int) None

Disable flags.

For valid flags, please see enable_only().

Examples:

# Only disable depth testing
ctx.disable(moderngl.DEPTH_TEST)

# Disable depth testing and face culling
ctx.disable(moderngl.DEPTH_TEST | moderngl.CULL_FACE)
Parameters

flag (int) – The flags to disable.

Context.enable_direct(enum: int) None

Gives direct access to glEnable so unsupported capabilities in ModernGL can be enabled.

Do not use this to set already supported context flags.

Example:

# Enum value from the opengl registry
GL_CONSERVATIVE_RASTERIZATION_NV = 0x9346
ctx.enable_direct(GL_CONSERVATIVE_RASTERIZATION_NV)
Context.disable_direct(enum: int) None

Gives direct access to glDisable so unsupported capabilities in ModernGL can be disabled.

Do not use this to set already supported context flags.

Example:

# Enum value from the opengl registry
GL_CONSERVATIVE_RASTERIZATION_NV = 0x9346
ctx.disable_direct(GL_CONSERVATIVE_RASTERIZATION_NV)
Context.finish() None

Wait for all drawing commands to finish.

Context.copy_buffer(dst: Buffer, src: Buffer, size: int = -1, *, read_offset: int = 0, write_offset: int = 0) None

Copy buffer content.

Parameters
  • dst (Buffer) – The destination buffer.

  • src (Buffer) – The source buffer.

  • size (int) – The number of bytes to copy.

Keyword Arguments
  • read_offset (int) – The read offset.

  • write_offset (int) – The write offset.

Context.copy_framebuffer(dst: Union[Framebuffer, Texture], src: Framebuffer) None

Copy framebuffer content.

Use this method to:

  • blit framebuffers.

  • copy framebuffer content into a texture.

  • downsample framebuffers. (it will allow to read the framebuffer’s content)

  • downsample a framebuffer directly to a texture.

Parameters
Context.detect_framebuffer(glo: Optional[int] = None) Framebuffer

Detect a framebuffer.

This is already done when creating a context, but if the underlying window library for some changes the default framebuffer during the lifetime of the application this might be necessary.

Parameters

glo (int) – Framebuffer object.

Returns

Framebuffer object

Context.gc() int

Deletes OpenGL objects.

This method must be called to garbage collect OpenGL resources when gc_mode is "context_gc"`.

Calling this method with any other gc_mode configuration has no effect and is perfectly safe.

Returns

Number of objects deleted

Return type

int

Context.__enter__()

Enters the context.

This should ideally be used with the with statement:

with other_context as ctx:
    # Do something in this context

When exiting the context the previously bound context is activated again.

Warning

Context switching can be risky unless you know what you are doing. Use with care.

Context.__exit__(exc_type, exc_val, exc_tb)

Exit the context.

See Context.__enter__()

Attributes

Context.gc_mode

The garbage collection mode.

The default mode is None meaning no automatic garbage collection is done. Other modes are auto and context_gc. Please see documentation for the appropriate configuration.

Examples:

# Disable automatic garbage collection.
# Each objects needs to be explicitly released.
ctx.gc_mode = None

# Collect all dead objects in the context and
# release them by calling Context.gc()
ctx.gc_mode = "context_gc"
ctx.gc()  # Deletes the collected objects

# Enable automatic garbage collection like
# we normally expect in python.
ctx.gc_mode = "auto"
Type

Optional[str]

Context.objects

Moderngl objects scheduled for deletion.

These are deleted when calling Context.gc().

Context.line_width

Set the default line width.

Warning

A line width other than 1.0 is not guaranteed to work across different OpenGL implementations. For wide lines you should be using geometry shaders.

Type

float

Context.point_size

Set/get the point size.

Point size changes the pixel size of rendered points. The min and max values are limited by POINT_SIZE_RANGE. This value usually at least (1, 100), but this depends on the drivers/vendors.

If variable point size is needed you can enable PROGRAM_POINT_SIZE and write to gl_PointSize in the vertex or geometry shader.

Note

Using a geometry shader to create triangle strips from points is often a safer way to render large points since you don’t have have any size restrictions.

Type

float

Context.depth_func

Set the default depth func.

Example:

ctx.depth_func = '<='  # GL_LEQUAL
ctx.depth_func = '<'   # GL_LESS
ctx.depth_func = '>='  # GL_GEQUAL
ctx.depth_func = '>'   # GL_GREATER
ctx.depth_func = '=='  # GL_EQUAL
ctx.depth_func = '!='  # GL_NOTEQUAL
ctx.depth_func = '0'   # GL_NEVER
ctx.depth_func = '1'   # GL_ALWAYS
Type

str

Context.blend_func

Set the blend func (write only).

Blend func can be set for rgb and alpha separately if needed.

Supported blend functions are:

moderngl.ZERO
moderngl.ONE
moderngl.SRC_COLOR
moderngl.ONE_MINUS_SRC_COLOR
moderngl.DST_COLOR
moderngl.ONE_MINUS_DST_COLOR
moderngl.SRC_ALPHA
moderngl.ONE_MINUS_SRC_ALPHA
moderngl.DST_ALPHA
moderngl.ONE_MINUS_DST_ALPHA

# Shortcuts
moderngl.DEFAULT_BLENDING     # (SRC_ALPHA, ONE_MINUS_SRC_ALPHA)
moderngl.ADDITIVE_BLENDING    # (ONE, ONE)
moderngl.PREMULTIPLIED_ALPHA  # (SRC_ALPHA, ONE)

Example:

# For both rgb and alpha
ctx.blend_func = moderngl.SRC_ALPHA, moderngl.ONE_MINUS_SRC_ALPHA

# Separate for rgb and alpha
ctx.blend_func = (
    moderngl.SRC_ALPHA, moderngl.ONE_MINUS_SRC_ALPHA,
    moderngl.ONE, moderngl.ONE
)
Type

tuple

Context.blend_equation

Set the blend equation (write only).

Blend equations specify how source and destination colors are combined in blending operations. By default FUNC_ADD is used.

Blend equation can be set for rgb and alpha separately if needed.

Supported functions are:

moderngl.FUNC_ADD               # source + destination
moderngl.FUNC_SUBTRACT          # source - destination
moderngl.FUNC_REVERSE_SUBTRACT  # destination - source
moderngl.MIN                    # Minimum of source and destination
moderngl.MAX                    # Maximum of source and destination

Example:

# For both rgb and alpha channel
ctx.blend_equation = moderngl.FUNC_ADD

# Separate for rgb and alpha channel
ctx.blend_equation = moderngl.FUNC_ADD, moderngl.MAX
Type

tuple

Context.viewport

Get or set the viewport of the active framebuffer.

Example:

>>> ctx.viewport
(0, 0, 1280, 720)
>>> ctx.viewport = (0, 0, 640, 360)
>>> ctx.viewport
(0, 0, 640, 360)

If no framebuffer is bound (0, 0, 0, 0) will be returned.

Type

tuple

Context.scissor

Get or set the scissor box for the active framebuffer.

When scissor testing is enabled fragments outside the defined scissor box will be discarded. This applies to rendered geometry or Context.clear().

Setting is value enables scissor testing in the framebuffer. Setting the scissor to None disables scissor testing and reverts the scissor box to match the framebuffer size.

Example:

# Enable scissor testing
>>> ctx.scissor = 100, 100, 200, 100
# Disable scissor testing
>>> ctx.scissor = None

If no framebuffer is bound (0, 0, 0, 0) will be returned.

Type

tuple

Context.version_code

The OpenGL version code. Reports 410 for OpenGL 4.1

Type

int

Context.screen

A Framebuffer instance representing the screen.

Normally set when creating a context with create_context() attaching to an existing context. This is the special system framebuffer represented by framebuffer id=0.

When creating a standalone context this property is not set since there are no default framebuffer.

Type

Framebuffer

Context.fbo

The active framebuffer. Set every time Framebuffer.use() is called.

Type

Framebuffer

Context.front_face

The front_face. Acceptable values are 'ccw' (default) or 'cw'.

Face culling must be enabled for this to have any effect: ctx.enable(moderngl.CULL_FACE).

Example:

# Triangles winded counter-clockwise considered front facing
ctx.front_face = 'ccw'
# Triangles winded clockwise considered front facing
ctx.front_face = 'cw'
Type

str

Context.cull_face

The face side to cull. Acceptable values are 'back' (default) 'front' or 'front_and_back'.

This is similar to Context.front_face()

Face culling must be enabled for this to have any effect: ctx.enable(moderngl.CULL_FACE).

Example:

ctx.cull_face = 'front'
ctx.cull_face = 'back'
ctx.cull_face = 'front_and_back'
Type

str

Context.wireframe

Wireframe settings for debugging.

Type

bool

Context.max_samples

The maximum supported number of samples for multisampling.

Type

int

Context.max_integer_samples

The max integer samples.

Type

int

Context.max_texture_units

The max texture units.

Type

int

Context.default_texture_unit

The default texture unit.

Type

int

Context.max_anisotropy

The maximum value supported for anisotropic filtering.

Type

float

Context.multisample

Enable/disable multisample mode (GL_MULTISAMPLE).

This property is write only.

Example:

# Enable
ctx.multisample = True
# Disable
ctx.multisample = False
Type

bool

Context.patch_vertices

The number of vertices that will be used to make up a single patch primitive.

Type

int

Context.provoking_vertex

Specifies the vertex to be used as the source of data for flat shaded varyings.

Flatshading a vertex shader varying output (ie. flat out vec3 pos) means to assign all vetices of the primitive the same value for that output. The vertex from which these values is derived is known as the provoking vertex.

It can be configured to be the first or the last vertex.

This property is write only.

Example:

# Use first vertex
ctx.provoking_vertex = moderngl.FIRST_VERTEX_CONVENTION

# Use last vertex
ctx.provoking_vertex = moderngl.LAST_VERTEX_CONVENTION
Type

int

Context.polygon_offset

Get or set the current polygon offset.

The tuple values represents two float values: unit and a factor:

ctx.polygon_offset = unit, factor

When drawing polygons, lines or points directly on top of exiting geometry the result is often not visually pleasant. We can experience z-fighting or partially fading fragments due to different primitives not being rasterized in the exact same way or simply depth buffer precision issues.

For example when visualizing polygons drawing a wireframe version on top of the original mesh, these issues are immediately apparent. Applying decals to surfaces is another common example.

The official documentation states the following:

When enabled, the depth value of each fragment is added
to a calculated offset value. The offset is added before
the depth test is performed and before the depth value
is written into the depth buffer. The offset value o is calculated by:
o = m * factor + r * units
where m is the maximum depth slope of the polygon and r is the smallest
value guaranteed to produce a resolvable difference in window coordinate
depth values. The value r is an implementation-specific constant.

In simpler terms: We use polygon offset to either add a positive offset to the geometry (push it away from you) or a negative offset to geometry (pull it towards you).

  • units is a constant offset to depth and will do the job alone if we are working with geometry parallel to the near/far plane.

  • The factor helps you handle sloped geometry (not parallel to near/far plane).

In most cases you can get away with [-1.0, 1.0] for both factor and units, but definitely play around with the values. When both values are set to 0 polygon offset is disabled internally.

To just get started with something you can try:

# Either push the geomtry away or pull it towards you
# with support for handling small to medium sloped geometry
ctx.polygon_offset = 1.0, 1.0
ctx.polygon_offset = -1.0, -1.0

# Disable polygon offset
ctx.polygon_offset = 0, 0
Type

tuple

Context.error

The result of glGetError() but human readable.

This values is provided for debug purposes only and is likely to reduce performace when used in a draw loop.

Type

str

Context.extensions

The extensions supported by the context.

All extensions names have a GL_ prefix, so if the spec refers to ARB_compute_shader we need to look for GL_ARB_compute_shader:

# If compute shaders are supported ...
>> "GL_ARB_compute_shader" in ctx.extensions
True

Example data:

{
    'GL_ARB_multi_bind',
    'GL_ARB_shader_objects',
    'GL_ARB_half_float_vertex',
    'GL_ARB_map_buffer_alignment',
    'GL_ARB_arrays_of_arrays',
    'GL_ARB_pipeline_statistics_query',
    'GL_ARB_provoking_vertex',
    'GL_ARB_gpu_shader5',
    'GL_ARB_uniform_buffer_object',
    'GL_EXT_blend_equation_separate',
    'GL_ARB_tessellation_shader',
    'GL_ARB_multi_draw_indirect',
    'GL_ARB_multisample',
    .. etc ..
}
Type

Set[str]

Context.info

OpenGL Limits and information about the context.

Example:

# The maximum width and height of a texture
>> ctx.info["GL_MAX_TEXTURE_SIZE"]
16384

# Vendor and renderer
>> ctx.info["GL_VENDOR"]
NVIDIA Corporation
>> ctx.info["GL_RENDERER"]
NVIDIA GeForce GT 650M OpenGL Engine

Example data:

{
    'GL_VENDOR': 'NVIDIA Corporation',
    'GL_RENDERER': 'NVIDIA GeForce GT 650M OpenGL Engine',
    'GL_VERSION': '4.1 NVIDIA-10.32.0 355.11.10.10.40.102',
    'GL_POINT_SIZE_RANGE': (1.0, 2047.0),
    'GL_SMOOTH_LINE_WIDTH_RANGE': (0.5, 1.0),
    'GL_ALIASED_LINE_WIDTH_RANGE': (1.0, 1.0),
    'GL_POINT_FADE_THRESHOLD_SIZE': 1.0,
    'GL_POINT_SIZE_GRANULARITY': 0.125,
    'GL_SMOOTH_LINE_WIDTH_GRANULARITY': 0.125,
    'GL_MIN_PROGRAM_TEXEL_OFFSET': -8.0,
    'GL_MAX_PROGRAM_TEXEL_OFFSET': 7.0,
    'GL_MINOR_VERSION': 1,
    'GL_MAJOR_VERSION': 4,
    'GL_SAMPLE_BUFFERS': 0,
    'GL_SUBPIXEL_BITS': 8,
    'GL_CONTEXT_PROFILE_MASK': 1,
    'GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT': 256,
    'GL_DOUBLEBUFFER': False,
    'GL_STEREO': False,
    'GL_MAX_VIEWPORT_DIMS': (16384, 16384),
    'GL_MAX_3D_TEXTURE_SIZE': 2048,
    'GL_MAX_ARRAY_TEXTURE_LAYERS': 2048,
    'GL_MAX_CLIP_DISTANCES': 8,
    'GL_MAX_COLOR_ATTACHMENTS': 8,
    'GL_MAX_COLOR_TEXTURE_SAMPLES': 8,
    'GL_MAX_COMBINED_FRAGMENT_UNIFORM_COMPONENTS': 233472,
    'GL_MAX_COMBINED_GEOMETRY_UNIFORM_COMPONENTS': 231424,
    'GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS': 80,
    'GL_MAX_COMBINED_UNIFORM_BLOCKS': 70,
    'GL_MAX_COMBINED_VERTEX_UNIFORM_COMPONENTS': 233472,
    'GL_MAX_CUBE_MAP_TEXTURE_SIZE': 16384,
    'GL_MAX_DEPTH_TEXTURE_SAMPLES': 8,
    'GL_MAX_DRAW_BUFFERS': 8,
    'GL_MAX_DUAL_SOURCE_DRAW_BUFFERS': 1,
    'GL_MAX_ELEMENTS_INDICES': 150000,
    'GL_MAX_ELEMENTS_VERTICES': 1048575,
    'GL_MAX_FRAGMENT_INPUT_COMPONENTS': 128,
    'GL_MAX_FRAGMENT_UNIFORM_COMPONENTS': 4096,
    'GL_MAX_FRAGMENT_UNIFORM_VECTORS': 1024,
    'GL_MAX_FRAGMENT_UNIFORM_BLOCKS': 14,
    'GL_MAX_GEOMETRY_INPUT_COMPONENTS': 128,
    'GL_MAX_GEOMETRY_OUTPUT_COMPONENTS': 128,
    'GL_MAX_GEOMETRY_TEXTURE_IMAGE_UNITS': 16,
    'GL_MAX_GEOMETRY_UNIFORM_BLOCKS': 14,
    'GL_MAX_GEOMETRY_UNIFORM_COMPONENTS': 2048,
    'GL_MAX_INTEGER_SAMPLES': 1,
    'GL_MAX_SAMPLES': 8,
    'GL_MAX_RECTANGLE_TEXTURE_SIZE': 16384,
    'GL_MAX_RENDERBUFFER_SIZE': 16384,
    'GL_MAX_SAMPLE_MASK_WORDS': 1,
    'GL_MAX_SERVER_WAIT_TIMEOUT': -1,
    'GL_MAX_TEXTURE_BUFFER_SIZE': 134217728,
    'GL_MAX_TEXTURE_IMAGE_UNITS': 16,
    'GL_MAX_TEXTURE_LOD_BIAS': 15,
    'GL_MAX_TEXTURE_SIZE': 16384,
    'GL_MAX_UNIFORM_BUFFER_BINDINGS': 70,
    'GL_MAX_UNIFORM_BLOCK_SIZE': 65536,
    'GL_MAX_VARYING_COMPONENTS': 0,
    'GL_MAX_VARYING_VECTORS': 31,
    'GL_MAX_VARYING_FLOATS': 0,
    'GL_MAX_VERTEX_ATTRIBS': 16,
    'GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS': 16,
    'GL_MAX_VERTEX_UNIFORM_COMPONENTS': 4096,
    'GL_MAX_VERTEX_UNIFORM_VECTORS': 1024,
    'GL_MAX_VERTEX_OUTPUT_COMPONENTS': 128,
    'GL_MAX_VERTEX_UNIFORM_BLOCKS': 14,
    'GL_MAX_VERTEX_ATTRIB_RELATIVE_OFFSET': 0,
    'GL_MAX_VERTEX_ATTRIB_BINDINGS': 0,
    'GL_VIEWPORT_BOUNDS_RANGE': (-32768, 32768),
    'GL_VIEWPORT_SUBPIXEL_BITS': 0,
    'GL_MAX_VIEWPORTS': 16
}
Type

dict

Context.mglo

Internal representation for debug purposes only.

Context.extra

Any - Attribute for storing user defined objects

Context Flags

Context flags are used to enable or disable states in the context. These are not the same enum values as in opengl, but are rather bit flags so we can or them together setting multiple states in a simple way.

These values are available in the Context object and in the moderngl module when you don’t have access to the context.

import moderngl

# From moderngl
ctx.enable_only(moderngl.DEPTH_TEST | moderngl.CULL_FACE)

# From context
ctx.enable_only(ctx.DEPTH_TEST | ctx.CULL_FACE)
Context.NOTHING = 0

Represents no states. Can be used with Context.enable_only() to disable all states.

Context.BLEND = 1

Enable/disable blending

Context.DEPTH_TEST = 2

Enable/disable depth testing

Context.CULL_FACE = 4

Enable/disable face culling

Context.RASTERIZER_DISCARD = 8

Enable/disable rasterization

Context.PROGRAM_POINT_SIZE = 16

Enables gl_PointSize in vertex or geometry shaders.

When enabled we can write to gl_PointSize in the vertex shader to specify the point size for each individual point.

If this value is not set in the shader the behavior is undefined. This means the points may or may not appear depending if the drivers enforce some default value for gl_PointSize.

When disabled Context.point_size is used.

Type

Context flag

Primitive Modes

Context.POINTS = 0

Each vertex represents a point

Context.LINES = 1

Vertices 0 and 1 are considered a line. Vertices 2 and 3 are considered a line. And so on. If the user specifies a non-even number of vertices, then the extra vertex is ignored.

Context.LINE_LOOP = 2

As line strips, except that the first and last vertices are also used as a line. Thus, you get n lines for n input vertices. If the user only specifies 1 vertex, the drawing command is ignored. The line between the first and last vertices happens after all of the previous lines in the sequence.

Context.LINE_STRIP = 3

The adjacent vertices are considered lines. Thus, if you pass n vertices, you will get n-1 lines. If the user only specifies 1 vertex, the drawing command is ignored.

Context.TRIANGLES = 4

Vertices 0, 1, and 2 form a triangle. Vertices 3, 4, and 5 form a triangle. And so on.

Context.TRIANGLE_STRIP = 5

Every group of 3 adjacent vertices forms a triangle. The face direction of the strip is determined by the winding of the first triangle. Each successive triangle will have its effective face order reversed, so the system compensates for that by testing it in the opposite way. A vertex stream of n length will generate n-2 triangles.

Context.TRIANGLE_FAN = 6

The first vertex is always held fixed. From there on, every group of 2 adjacent vertices form a triangle with the first. So with a vertex stream, you get a list of triangles like so: (0, 1, 2) (0, 2, 3), (0, 3, 4), etc. A vertex stream of n length will generate n-2 triangles.

Context.LINES_ADJACENCY = 10

These are special primitives that are expected to be used specifically with geomtry shaders. These primitives give the geometry shader more vertices to work with for each input primitive. Data needs to be duplicated in buffers.

Context.LINE_STRIP_ADJACENCY = 11

These are special primitives that are expected to be used specifically with geomtry shaders. These primitives give the geometry shader more vertices to work with for each input primitive. Data needs to be duplicated in buffers.

Context.TRIANGLES_ADJACENCY = 12

These are special primitives that are expected to be used specifically with geomtry shaders. These primitives give the geometry shader more vertices to work with for each input primitive. Data needs to be duplicated in buffers.

Context.TRIANGLE_STRIP_ADJACENCY = 13

These are special primitives that are expected to be used specifically with geomtry shaders. These primitives give the geometry shader more vertices to work with for each input primitive. Data needs to be duplicated in buffers.

Context.PATCHES = 14

primitive type can only be used when Tessellation is active. It is a primitive with a user-defined number of vertices, which is then tessellated based on the control and evaluation shaders into regular points, lines, or triangles, depending on the TES’s settings.

Texture Filters

Also available in the Context instance including mode details.

Context.NEAREST = 9728

Returns the value of the texture element that is nearest (in Manhattan distance) to the specified texture coordinates.

Context.LINEAR = 9729

Returns the weighted average of the four texture elements that are closest to the specified texture coordinates. These can include items wrapped or repeated from other parts of a texture, depending on the values of texture repeat mode, and on the exact mapping.

Context.NEAREST_MIPMAP_NEAREST = 9984

Chooses the mipmap that most closely matches the size of the pixel being textured and uses the NEAREST criterion (the texture element closest to the specified texture coordinates) to produce a texture value.

Context.LINEAR_MIPMAP_NEAREST = 9985

Chooses the mipmap that most closely matches the size of the pixel being textured and uses the LINEAR criterion (a weighted average of the four texture elements that are closest to the specified texture coordinates) to produce a texture value.

Context.NEAREST_MIPMAP_LINEAR = 9986

Chooses the two mipmaps that most closely match the size of the pixel being textured and uses the NEAREST criterion (the texture element closest to the specified texture coordinates ) to produce a texture value from each mipmap. The final texture value is a weighted average of those two values.

Context.LINEAR_MIPMAP_LINEAR = 9987

Chooses the two mipmaps that most closely match the size of the pixel being textured and uses the LINEAR criterion (a weighted average of the texture elements that are closest to the specified texture coordinates) to produce a texture value from each mipmap. The final texture value is a weighted average of those two values.

Blend Functions

Blend functions are used with Context.blend_func to control blending operations.

# Default value
ctx.blend_func = ctx.SRC_ALPHA, ctx.ONE_MINUS_SRC_ALPHA
Context.ZERO = 0

(0,0,0,0)

Context.ONE = 1

(1,1,1,1)

Context.SRC_COLOR = 768

(Rs0/kR,Gs0/kG,Bs0/kB,As0/kA)

Context.ONE_MINUS_SRC_COLOR = 769

(1,1,1,1) − (Rs0/kR,Gs0/kG,Bs0/kB,As0/kA)

Context.SRC_ALPHA = 770

(As0/kA,As0/kA,As0/kA,As0/kA)

Context.ONE_MINUS_SRC_ALPHA = 771

(1,1,1,1) − (As0/kA,As0/kA,As0/kA,As0/kA)

Context.DST_ALPHA = 772

(Ad/kA,Ad/kA,Ad/kA,Ad/kA)

Context.ONE_MINUS_DST_ALPHA = 773

(1,1,1,1) − (Ad/kA,Ad/kA,Ad/kA,Ad/kA)

Context.DST_COLOR = 774

(Rd/kR,Gd/kG,Bd/kB,Ad/kA)

Context.ONE_MINUS_DST_COLOR = 775

(1,1,1,1) − (Rd/kR,Gd/kG,Bd/kB,Ad/kA)

Blend Function Shortcuts

Context.DEFAULT_BLENDING = (770, 771)

Shotcut for the default blending SRC_ALPHA, ONE_MINUS_SRC_ALPHA

Context.ADDITIVE_BLENDING = (1, 1)

Shotcut for additive blending ONE, ONE

Context.PREMULTIPLIED_ALPHA = (770, 1)

Shotcut for blend mode when using premultiplied alpha SRC_ALPHA, ONE

Blend Equations

Used with Context.blend_equation.

Context.FUNC_ADD = 32774

source + destination

Context.FUNC_SUBTRACT = 32778

source - destination

Context.FUNC_REVERSE_SUBTRACT = 32779

destination - source

Context.MIN = 32775

Minimum of source and destination

Context.MAX = 32776

Maximum of source and destination

Other Enums

Context.FIRST_VERTEX_CONVENTION = 36429

Specifies the first vertex should be used as the source of data for flat shaded varyings. Used with Context.provoking_vertex.

Context.LAST_VERTEX_CONVENTION = 36430

Specifies the last vertex should be used as the source of data for flat shaded varyings. Used with Context.provoking_vertex.

Examples

ModernGL Context

import moderngl
# create a window
ctx = moderngl.create_context()
print(ctx.version_code)

Standalone ModernGL Context

import moderngl
ctx = moderngl.create_standalone_context()
print(ctx.version_code)

ContextManager

context_manager.py

 1import moderngl
 2
 3
 4class ContextManager:
 5    ctx = None
 6
 7    @staticmethod
 8    def get_default_context(allow_fallback_standalone_context=True) -> moderngl.Context:
 9        '''
10            Default context
11        '''
12
13        if ContextManager.ctx is None:
14            try:
15                ContextManager.ctx = moderngl.create_context()
16            except:
17                if allow_fallback_standalone_context:
18                    ContextManager.ctx = moderngl.create_standalone_context()
19                else:
20                    raise
21
22        return ContextManager.ctx

example.py

1from context_manager import ContextManager
2
3ctx = ContextManager.get_default_context()
4print(ctx.version_code)