Module glium::draw_parameters

Describes miscellaneous parameters to be used when drawing.

Example

let params = glium::DrawParameters {
    depth_test: glium::draw_parameters::DepthTest::IfLess,
    depth_write: true,
    scissor: Some(glium::Rect { bottom: 0, left: 100, width: 100, height: 200 }),
    .. Default::default()
};

The new API

A new API is currently in construction. Example:

let params = glium::DrawParameters::new(&display)
                .with_rasterizer_discard_if_supported().unwrap()
                .With_scissor(glium::Rect { bottom: 0, left: 100, width: 100, height: 200 });

Instead of the draw command generating errors because of non-supported parameters, the errors will be generated directly when creating the parameters.

Queries

Query objects allow you to obtain information about the rendering process. For example, a SamplesPassedQuery allows you to know the number of samples that have been drawn.

let query = glium::draw_parameters::SamplesPassedQuery::new(&display).unwrap();
let params = glium::DrawParameters {
    samples_passed_query: Some((&query).into()),
    .. Default::default()
};

After drawing with these parameters, you can retreive the value inside the query:

let value = query.get();

This operation will consume the query and block until the GPU has finished drawing. Instead, you can also use the query as a condition for drawing:

let params = glium::DrawParameters {
    condition: Some(glium::draw_parameters::ConditionalRendering {
        query: (&query).into(),
        wait: true,
        per_region: true,
    }),
    .. Default::default()
};

If you use conditional rendering, glium will submit the draw command but the GPU will execute it only if the query contains a value different from 0.

WrongQueryOperation errors

OpenGL puts some restrictions about the usage of queries. If you draw one or several times with a query, then draw without that query, then the query cannot be used again. Trying to draw with it results in a WrongQueryOperation error returned by the draw function.

For the same reasons, as soon as you call is_ready on a query it will stop being usable.

Structs

AnySamplesPassedQuery	A query type that allows you to know whether any sample has been written to the output during the operations executed with this query.
ConditionalRendering	Condition whether to render or not.
DrawParameters	Represents the parameters to use when drawing.
DrawParametersBuilder	This is what the new API of DrawParameters will look like in a future version.
PrimitivesGeneratedQuery	Query that allows you to know the number of primitives generated by the geometry shader. Will stay at 0 if you use it without any active geometry shader.
SamplesPassedQuery	A query that allows you to know the number of samples written to the output during the draw operations where this query was active.
TimeElapsedQuery	A query that allows you to know the number of nanoseconds that have elapsed during the draw operations.
TransformFeedbackPrimitivesWrittenQuery	Query that allows you to know the number of primitives generated by transform feedback.

Enums

BackfaceCullingMode	Describes how triangles should be filtered before the fragment processing. Backface culling is purely an optimization. If you don't know what this does, just use CullingDisabled.
BlendingFunction	Function that the GPU will use for blending.
DepthTest	The function that the GPU will use to determine whether to write over an existing pixel on the target.
LinearBlendingFactor	Indicates which value to multiply each component with.
PolygonMode	Defines how the device should render polygons.
QueryCreationError	Error that can happen when creating a query object.
SamplesQueryParam	The query to use for samples counting.
Smooth	Specifies a hint for the smoothing.
StencilOperation	Specificies which operation the GPU will do depending on the result of the stencil test.
StencilTest	Specifies which comparison the GPU will do to determine whether a sample passes the stencil test. The general equation is (ref & mask) CMP (stencil & mask), where ref is the reference value (stencil_reference_value_clockwise or stencil_reference_value_counter_clockwise), CMP is the comparison chosen, and stencil is the current value in the stencil buffer.

Functions

validate

Checks parameters and panics if something is wrong.