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use crate::context::CommandContext;
use crate::version::Api;
use crate::version::Version;
use crate::DrawError;
use crate::gl;
/// Represents the depth parameters of a draw command.
#[derive(Debug, Copy, Clone)]
pub struct Depth {
/// The function that the GPU will use to determine whether to write over an existing pixel
/// on the target. Don't forget to set `depth_write` appropriately if you use a depth test.
///
/// See the `DepthTest` documentation for more details.
///
/// The default is `Overwrite`.
pub test: DepthTest,
/// Sets whether the GPU will write the depth values on the depth buffer if they pass the
/// depth test.
///
/// The default is `false`. You most likely want `true` if you're doing depth testing.
///
/// If you pass `true` but don't have a depth buffer available, drawing will produce
/// a `NoDepthBuffer` error.
pub write: bool,
/// The range of possible Z values in surface coordinates.
///
/// Just like OpenGL turns X and Y coordinates between `-1.0` and `1.0` into surface
/// coordinates, it will also map your Z coordinates to a certain range which you can
/// specify here.
///
/// The two values must be between `0.0` and `1.0`, anything outside this range will result
/// in a panic. By default the depth range is `(0.0, 1.0)`.
///
/// The first value of the tuple must be the "near" value, where `-1.0` will be mapped.
/// The second value must be the "far" value, where `1.0` will be mapped.
/// It is possible for the "near" value to be greater than the "far" value.
pub range: (f32, f32),
/// Sets whether the depth values of samples should be clamped to `0.0` and `1.0`.
///
/// The default value is `NoClamp`.
pub clamp: DepthClamp,
}
impl Default for Depth {
#[inline]
fn default() -> Depth {
Depth {
test: DepthTest::Overwrite,
write: false,
range: (0.0, 1.0),
clamp: DepthClamp::NoClamp,
}
}
}
/// The function that the GPU will use to determine whether to write over an existing pixel
/// on the target.
///
/// # Depth buffers
///
/// After the fragment shader has been run, the GPU maps the output Z coordinates to the depth
/// range (which you can specify in the draw parameters) in order to obtain the depth value in
/// in window coordinates. This depth value is always between `0.0` and `1.0`.
///
/// In addition to the buffer where pixel colors are stored, you can also have a buffer
/// which contains the depth value of each pixel. Whenever the GPU tries to write a pixel,
/// it will first compare the depth value of the pixel to be written with the depth value that
/// is stored at this location. If `depth_write` is set to `true` in the draw parameters, it will
/// then write the depth value in the buffer.
///
/// The most common value for depth testing is to set `depth_test` to `IfLess`, and `depth_write`
/// to `true`.
///
/// If you don't have a depth buffer available, you can only pass `Overwrite`. Glium detects if
/// you pass any other value and reports an error.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum DepthTest {
/// Never replace the target pixel.
///
/// This option doesn't really make sense, but is here for completeness.
Ignore,
/// Always replace the target pixel.
///
/// This is the default mode.
Overwrite,
/// Replace if the z-value of the source is equal to the destination.
IfEqual,
/// Replace if the z-value of the source is different than the destination.
IfNotEqual,
/// Replace if the z-value of the source is more than the destination.
IfMore,
/// Replace if the z-value of the source is more than, or equal to the destination.
IfMoreOrEqual,
/// Replace if the z-value of the source is less than the destination.
IfLess,
/// Replace if the z-value of the source is less than, or equal to the destination.
IfLessOrEqual
}
impl DepthTest {
/// Returns true if the function requires a depth buffer to be used.
#[inline]
pub fn requires_depth_buffer(&self) -> bool {
match *self {
DepthTest::Ignore => true,
DepthTest::Overwrite => false,
DepthTest::IfEqual => true,
DepthTest::IfNotEqual => true,
DepthTest::IfMore => true,
DepthTest::IfMoreOrEqual => true,
DepthTest::IfLess => true,
DepthTest::IfLessOrEqual => true,
}
}
#[inline]
fn to_glenum(&self) -> gl::types::GLenum {
match *self {
DepthTest::Ignore => gl::NEVER,
DepthTest::Overwrite => gl::ALWAYS,
DepthTest::IfEqual => gl::EQUAL,
DepthTest::IfNotEqual => gl::NOTEQUAL,
DepthTest::IfMore => gl::GREATER,
DepthTest::IfMoreOrEqual => gl::GEQUAL,
DepthTest::IfLess => gl::LESS,
DepthTest::IfLessOrEqual => gl::LEQUAL,
}
}
}
/// Specifies whether the depth value of samples should be clamped to `0.0` or `1.0`.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum DepthClamp {
/// Do not clamp. Samples with values outside of the `[0.0, 1.0]` range will be discarded.
///
/// This is the default value and is supported everywhere.
NoClamp,
/// Clamp the depth values. All samples will always be drawn.
///
/// This value is only supported on OpenGL.
Clamp,
/// Depth values inferior to `0.0` will be clamped to `0.0`.
///
/// **This option is supported only by very few OpenGL devices**.
ClampNear,
/// Depth values superior to `1.0` will be clamped to `1.0`.
///
/// **This option is supported only by very few OpenGL devices**.
ClampFar,
}
pub fn sync_depth(ctxt: &mut CommandContext<'_>, depth: &Depth) -> Result<(), DrawError> {
// depth clamp
{
let state = &mut *ctxt.state;
match (depth.clamp, &mut state.enabled_depth_clamp_near,
&mut state.enabled_depth_clamp_far)
{
(DepthClamp::NoClamp, &mut false, &mut false) => (),
(DepthClamp::Clamp, &mut true, &mut true) => (),
(DepthClamp::NoClamp, near, far) => {
if ctxt.version >= &Version(Api::Gl, 3, 0) || ctxt.extensions.gl_arb_depth_clamp ||
ctxt.extensions.gl_nv_depth_clamp
{
unsafe { ctxt.gl.Disable(gl::DEPTH_CLAMP) };
*near = false;
*far = false;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
(DepthClamp::Clamp, near, far) => {
if ctxt.version >= &Version(Api::Gl, 3, 0) || ctxt.extensions.gl_arb_depth_clamp ||
ctxt.extensions.gl_nv_depth_clamp
{
unsafe { ctxt.gl.Enable(gl::DEPTH_CLAMP) };
*near = true;
*far = true;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
(DepthClamp::ClampNear, &mut true, &mut false) => (),
(DepthClamp::ClampFar, &mut false, &mut true) => (),
(DepthClamp::ClampNear, &mut true, far) => {
if ctxt.extensions.gl_amd_depth_clamp_separate {
unsafe { ctxt.gl.Disable(gl::DEPTH_CLAMP_FAR_AMD) };
*far = false;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
(DepthClamp::ClampNear, near @ &mut false, far) => {
if ctxt.extensions.gl_amd_depth_clamp_separate {
unsafe { ctxt.gl.Enable(gl::DEPTH_CLAMP_NEAR_AMD) };
if *far { unsafe { ctxt.gl.Disable(gl::DEPTH_CLAMP_FAR_AMD); } }
*near = true;
*far = false;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
(DepthClamp::ClampFar, near, &mut true) => {
if ctxt.extensions.gl_amd_depth_clamp_separate {
unsafe { ctxt.gl.Disable(gl::DEPTH_CLAMP_NEAR_AMD) };
*near = false;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
(DepthClamp::ClampFar, near, far @ &mut false) => {
if ctxt.extensions.gl_amd_depth_clamp_separate {
unsafe { ctxt.gl.Enable(gl::DEPTH_CLAMP_FAR_AMD) };
if *near { unsafe { ctxt.gl.Disable(gl::DEPTH_CLAMP_NEAR_AMD); } }
*near = false;
*far = true;
} else {
return Err(DrawError::DepthClampNotSupported);
}
},
}
}
// depth range
if depth.range.0 < 0.0 || depth.range.0 > 1.0 ||
depth.range.1 < 0.0 || depth.range.1 > 1.0
{
return Err(DrawError::InvalidDepthRange);
}
if depth.range != ctxt.state.depth_range {
// TODO: WebGL requires depth.range.1 > depth.range.0
unsafe {
ctxt.gl.DepthRange(depth.range.0 as f64, depth.range.1 as f64);
}
ctxt.state.depth_range = depth.range;
}
if depth.test == DepthTest::Overwrite && !depth.write {
// simply disabling GL_DEPTH_TEST
if ctxt.state.enabled_depth_test {
unsafe { ctxt.gl.Disable(gl::DEPTH_TEST) };
ctxt.state.enabled_depth_test = false;
}
return Ok(());
} else if !ctxt.state.enabled_depth_test {
unsafe { ctxt.gl.Enable(gl::DEPTH_TEST) };
ctxt.state.enabled_depth_test = true;
}
// depth test
unsafe {
let depth_test = depth.test.to_glenum();
if ctxt.state.depth_func != depth_test {
ctxt.gl.DepthFunc(depth_test);
ctxt.state.depth_func = depth_test;
}
}
// depth mask
if depth.write != ctxt.state.depth_mask {
unsafe {
ctxt.gl.DepthMask(if depth.write { gl::TRUE } else { gl::FALSE });
}
ctxt.state.depth_mask = depth.write;
}
Ok(())
}