src/tests/end2end/DepthBiasTests.cpp - dawn - Git at Google

 // Copyright 2020 The Dawn Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #include "common/Constants.h"
 #include "common/Math.h"
 #include "tests/DawnTest.h"
 #include "utils/ComboRenderPipelineDescriptor.h"
 #include "utils/TextureFormatUtils.h"
 #include "utils/WGPUHelpers.h"

 constexpr static unsigned int kRTSize = 2;

 enum class QuadAngle { Flat, TiltedX };

 class DepthBiasTests : public DawnTest {
   protected:
     void RunDepthBiasTest(wgpu::TextureFormat depthFormat,
                           float depthClear,
                           QuadAngle quadAngle,
                           int32_t bias,
                           float biasSlopeScale,
                           float biasClamp) {
         const char* vertexSource = nullptr;
         switch (quadAngle) {
             case QuadAngle::Flat:
                 // Draw a square at z = 0.25
                 vertexSource = R"(
     [[stage(vertex)]]
     fn main([[builtin(vertex_index)]] VertexIndex : u32) -> [[builtin(position)]] vec4<f32> {
         let pos : array<vec2<f32>, 6> = array<vec2<f32>, 6>(
             vec2<f32>(-1.0, -1.0),
             vec2<f32>( 1.0, -1.0),
             vec2<f32>(-1.0,  1.0),
             vec2<f32>(-1.0,  1.0),
             vec2<f32>( 1.0, -1.0),
             vec2<f32>( 1.0,  1.0));
         return vec4<f32>(pos[VertexIndex], 0.25, 1.0);
     })";
                 break;

             case QuadAngle::TiltedX:
                 // Draw a square ranging from 0 to 0.5, bottom to top
                 vertexSource = R"(
     [[stage(vertex)]]
     fn main([[builtin(vertex_index)]] VertexIndex : u32) -> [[builtin(position)]] vec4<f32> {
         let pos : array<vec3<f32>, 6> = array<vec3<f32>, 6>(
             vec3<f32>(-1.0, -1.0, 0.0),
             vec3<f32>( 1.0, -1.0, 0.0),
             vec3<f32>(-1.0,  1.0, 0.5),
             vec3<f32>(-1.0,  1.0, 0.5),
             vec3<f32>( 1.0, -1.0, 0.0),
             vec3<f32>( 1.0,  1.0, 0.5));
         return vec4<f32>(pos[VertexIndex], 1.0);
     })";
                 break;
         }

         wgpu::ShaderModule vertexModule = utils::CreateShaderModule(device, vertexSource);

         wgpu::ShaderModule fragmentModule = utils::CreateShaderModule(device, R"(
     [[stage(fragment)]] fn main() -> [[location(0)]] vec4<f32> {
         return vec4<f32>(1.0, 0.0, 0.0, 1.0);
     })");

         {
             wgpu::TextureDescriptor descriptor;
             descriptor.size = {kRTSize, kRTSize, 1};
             descriptor.format = depthFormat;
             descriptor.usage = wgpu::TextureUsage::RenderAttachment | wgpu::TextureUsage::CopySrc;
             mDepthTexture = device.CreateTexture(&descriptor);
         }

         {
             wgpu::TextureDescriptor descriptor;
             descriptor.size = {kRTSize, kRTSize, 1};
             descriptor.format = wgpu::TextureFormat::RGBA8Unorm;
             descriptor.usage = wgpu::TextureUsage::RenderAttachment | wgpu::TextureUsage::CopySrc;
             mRenderTarget = device.CreateTexture(&descriptor);
         }

         // Create a render pass which clears depth to depthClear
         utils::ComboRenderPassDescriptor renderPassDesc({mRenderTarget.CreateView()},
                                                         mDepthTexture.CreateView());
         renderPassDesc.cDepthStencilAttachmentInfo.clearDepth = depthClear;

         // Create a render pipeline to render the quad
         utils::ComboRenderPipelineDescriptor2 renderPipelineDesc;

         renderPipelineDesc.vertex.module = vertexModule;
         renderPipelineDesc.cFragment.module = fragmentModule;
         wgpu::DepthStencilState* depthStencil = renderPipelineDesc.EnableDepthStencil(depthFormat);
         depthStencil->depthWriteEnabled = true;
         depthStencil->depthBias = bias;
         depthStencil->depthBiasSlopeScale = biasSlopeScale;
         depthStencil->depthBiasClamp = biasClamp;

         if (depthFormat != wgpu::TextureFormat::Depth32Float) {
             depthStencil->depthCompare = wgpu::CompareFunction::Greater;
         }

         wgpu::RenderPipeline pipeline = device.CreateRenderPipeline2(&renderPipelineDesc);

         // Draw the quad (two triangles)
         wgpu::CommandEncoder commandEncoder = device.CreateCommandEncoder();
         wgpu::RenderPassEncoder pass = commandEncoder.BeginRenderPass(&renderPassDesc);
         pass.SetPipeline(pipeline);
         pass.Draw(6);
         pass.EndPass();

         wgpu::CommandBuffer commands = commandEncoder.Finish();
         queue.Submit(1, &commands);
     }

     // Floating point depth buffers use the following formula to calculate bias
     // bias = depthBias * 2 ** (exponent(max z of primitive) - number of bits in mantissa) +
     //        slopeScale * maxSlope
     // https://docs.microsoft.com/en-us/windows/win32/direct3d11/d3d10-graphics-programming-guide-output-merger-stage-depth-bias
     // https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/vkCmdSetDepthBias.html
     // https://developer.apple.com/documentation/metal/mtlrendercommandencoder/1516269-setdepthbias
     //
     // To get a final bias of 0.25 for primitives with z = 0.25, we can use
     // depthBias = 0.25 / (2 ** (-2 - 23)) = 8388608
     static constexpr int32_t kPointTwoFiveBiasForPointTwoFiveZOnFloat = 8388608;

     wgpu::Texture mDepthTexture;
     wgpu::Texture mRenderTarget;
 };

 // Test adding positive bias to output
 TEST_P(DepthBiasTests, PositiveBiasOnFloat) {
     // NVIDIA GPUs under Vulkan seem to be using a different scale than everyone else.
     DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

     // OpenGL uses a different scale than the other APIs
     DAWN_SKIP_TEST_IF(IsOpenGL());
     DAWN_SKIP_TEST_IF(IsOpenGLES());

     // Draw quad flat on z = 0.25 with 0.25 bias
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
                      kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0);

     // Quad at z = 0.25 + 0.25 bias = 0.5
     std::vector<float> expected = {
         0.5, 0.5,  //
         0.5, 0.5,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding positive bias to output with a clamp
 TEST_P(DepthBiasTests, PositiveBiasOnFloatWithClamp) {
     // Clamping support in OpenGL is spotty
     DAWN_SKIP_TEST_IF(IsOpenGL());
     DAWN_SKIP_TEST_IF(IsOpenGLES());

     // Draw quad flat on z = 0.25 with 0.25 bias clamped at 0.125.
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
                      kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0.125);

     // Quad at z = 0.25 + min(0.25 bias, 0.125 clamp) = 0.375
     std::vector<float> expected = {
         0.375, 0.375,  //
         0.375, 0.375,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding negative bias to output
 TEST_P(DepthBiasTests, NegativeBiasOnFloat) {
     // NVIDIA GPUs seems to be using a different scale than everyone else
     DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

     // OpenGL uses a different scale than the other APIs
     DAWN_SKIP_TEST_IF(IsOpenGL());

     // Draw quad flat on z = 0.25 with -0.25 bias, depth clear of 0.125
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::Flat,
                      -kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0);

     // Quad at z = 0.25 - 0.25 bias = 0
     std::vector<float> expected = {
         0.0, 0.0,  //
         0.0, 0.0,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding negative bias to output with a clamp
 TEST_P(DepthBiasTests, NegativeBiasOnFloatWithClamp) {
     // Clamping support in OpenGL is spotty
     DAWN_SKIP_TEST_IF(IsOpenGL());
     DAWN_SKIP_TEST_IF(IsOpenGLES());

     // Draw quad flat on z = 0.25 with -0.25 bias clamped at -0.125.
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
                      -kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, -0.125);

     // Quad at z = 0.25 + max(-0.25 bias, -0.125 clamp) = 0.125
     std::vector<float> expected = {
         0.125, 0.125,  //
         0.125, 0.125,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding positive infinite slope bias to output
 TEST_P(DepthBiasTests, PositiveInfinitySlopeBiasOnFloat) {
     // NVIDIA GPUs do not clamp values to 1 when using Inf slope bias.
     DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

     // Draw quad with z from 0 to 0.5 with inf slope bias
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::TiltedX, 0,
                      std::numeric_limits<float>::infinity(), 0);

     // Value at the center of the pixel + (0.25 slope * Inf slope bias) = 1 (clamped)
     std::vector<float> expected = {
         1.0, 1.0,  //
         1.0, 1.0,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding positive infinite slope bias to output
 TEST_P(DepthBiasTests, NegativeInfinityBiasOnFloat) {
     // NVIDIA GPUs do not clamp values to 0 when using -Inf slope bias.
     DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

     // Draw quad with z from 0 to 0.5 with -inf slope bias
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::TiltedX, 0,
                      -std::numeric_limits<float>::infinity(), 0);

     // Value at the center of the pixel + (0.25 slope * -Inf slope bias) = 0 (clamped)
     std::vector<float> expected = {
         0.0, 0.0,  //
         0.0, 0.0,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test tiledX quad with no bias
 TEST_P(DepthBiasTests, NoBiasTiltedXOnFloat) {
     // Draw quad with z from 0 to 0.5 with no bias
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, 0, 0);

     // Depth values of TiltedX quad. Values at the center of the pixels.
     std::vector<float> expected = {
         0.375, 0.375,  //
         0.125, 0.125,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding positive slope bias to output
 TEST_P(DepthBiasTests, PositiveSlopeBiasOnFloat) {
     // Draw quad with z from 0 to 0.5 with a slope bias of 1
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, 1, 0);

     // Value at the center of the pixel + (0.25 slope * 1.0 slope bias)
     std::vector<float> expected = {
         0.625, 0.625,  //
         0.375, 0.375,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding negative half slope bias to output
 TEST_P(DepthBiasTests, NegativeHalfSlopeBiasOnFloat) {
     // Draw quad with z from 0 to 0.5 with a slope bias of -0.5
     RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, -0.5, 0);

     // Value at the center of the pixel + (0.25 slope * -0.5 slope bias)
     std::vector<float> expected = {
         0.25, 0.25,  //
         0.0, 0.0,    //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
                       wgpu::TextureAspect::DepthOnly);
 }

 // Test adding positive bias to output
 TEST_P(DepthBiasTests, PositiveBiasOn24bit) {
     // Draw quad flat on z = 0.25 with 0.25 bias
     RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::Flat,
                      0.25f * (1 << 25), 0, 0);

     // Only the bottom left quad has colors. 0.5 quad > 0.4 clear.
     // TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
     std::vector<RGBA8> expected = {
         RGBA8::kRed, RGBA8::kRed,  //
         RGBA8::kRed, RGBA8::kRed,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
 }

 // Test adding positive bias to output with a clamp
 TEST_P(DepthBiasTests, PositiveBiasOn24bitWithClamp) {
     // Clamping support in OpenGL is spotty
     DAWN_SKIP_TEST_IF(IsOpenGL());
     DAWN_SKIP_TEST_IF(IsOpenGLES());

     // Draw quad flat on z = 0.25 with 0.25 bias clamped at 0.125.
     RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::Flat,
                      0.25f * (1 << 25), 0, 0.1f);

     // Since we cleared with a depth of 0.4 and clamped bias at 0.4, the depth test will fail. 0.25
     // + 0.125 < 0.4 clear.
     // TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
     std::vector<RGBA8> zero = {
         RGBA8::kZero, RGBA8::kZero,  //
         RGBA8::kZero, RGBA8::kZero,  //
     };

     EXPECT_TEXTURE_EQ(zero.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
 }

 // Test adding positive bias to output
 TEST_P(DepthBiasTests, PositiveSlopeBiasOn24bit) {
     // Draw quad with z from 0 to 0.5 with a slope bias of 1
     RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::TiltedX, 0, 1, 0);

     // Only the top half of the quad has a depth > 0.4 clear
     // TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
     std::vector<RGBA8> expected = {
         RGBA8::kRed, RGBA8::kRed,    //
         RGBA8::kZero, RGBA8::kZero,  //
     };

     EXPECT_TEXTURE_EQ(expected.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
 }

 DAWN_INSTANTIATE_TEST(DepthBiasTests,
                       D3D12Backend(),
                       MetalBackend(),
                       OpenGLBackend(),
                       OpenGLESBackend(),
                       VulkanBackend());
	// Copyright 2020 The Dawn Authors
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#include "common/Constants.h"
	#include "common/Math.h"
	#include "tests/DawnTest.h"
	#include "utils/ComboRenderPipelineDescriptor.h"
	#include "utils/TextureFormatUtils.h"
	#include "utils/WGPUHelpers.h"

	constexpr static unsigned int kRTSize = 2;

	enum class QuadAngle { Flat, TiltedX };

	class DepthBiasTests : public DawnTest {
	protected:
	void RunDepthBiasTest(wgpu::TextureFormat depthFormat,
	float depthClear,
	QuadAngle quadAngle,
	int32_t bias,
	float biasSlopeScale,
	float biasClamp) {
	const char* vertexSource = nullptr;
	switch (quadAngle) {
	case QuadAngle::Flat:
	// Draw a square at z = 0.25
	vertexSource = R"(
	[[stage(vertex)]]
	fn main([[builtin(vertex_index)]] VertexIndex : u32) -> [[builtin(position)]] vec4<f32> {
	let pos : array<vec2<f32>, 6> = array<vec2<f32>, 6>(
	vec2<f32>(-1.0, -1.0),
	vec2<f32>( 1.0, -1.0),
	vec2<f32>(-1.0, 1.0),
	vec2<f32>(-1.0, 1.0),
	vec2<f32>( 1.0, -1.0),
	vec2<f32>( 1.0, 1.0));
	return vec4<f32>(pos[VertexIndex], 0.25, 1.0);
	})";
	break;

	case QuadAngle::TiltedX:
	// Draw a square ranging from 0 to 0.5, bottom to top
	vertexSource = R"(
	[[stage(vertex)]]
	fn main([[builtin(vertex_index)]] VertexIndex : u32) -> [[builtin(position)]] vec4<f32> {
	let pos : array<vec3<f32>, 6> = array<vec3<f32>, 6>(
	vec3<f32>(-1.0, -1.0, 0.0),
	vec3<f32>( 1.0, -1.0, 0.0),
	vec3<f32>(-1.0, 1.0, 0.5),
	vec3<f32>(-1.0, 1.0, 0.5),
	vec3<f32>( 1.0, -1.0, 0.0),
	vec3<f32>( 1.0, 1.0, 0.5));
	return vec4<f32>(pos[VertexIndex], 1.0);
	})";
	break;
	}

	wgpu::ShaderModule vertexModule = utils::CreateShaderModule(device, vertexSource);

	wgpu::ShaderModule fragmentModule = utils::CreateShaderModule(device, R"(
	[[stage(fragment)]] fn main() -> [[location(0)]] vec4<f32> {
	return vec4<f32>(1.0, 0.0, 0.0, 1.0);
	})");

	{
	wgpu::TextureDescriptor descriptor;
	descriptor.size = {kRTSize, kRTSize, 1};
	descriptor.format = depthFormat;
	descriptor.usage = wgpu::TextureUsage::RenderAttachment \| wgpu::TextureUsage::CopySrc;
	mDepthTexture = device.CreateTexture(&descriptor);
	}

	{
	wgpu::TextureDescriptor descriptor;
	descriptor.size = {kRTSize, kRTSize, 1};
	descriptor.format = wgpu::TextureFormat::RGBA8Unorm;
	descriptor.usage = wgpu::TextureUsage::RenderAttachment \| wgpu::TextureUsage::CopySrc;
	mRenderTarget = device.CreateTexture(&descriptor);
	}

	// Create a render pass which clears depth to depthClear
	utils::ComboRenderPassDescriptor renderPassDesc({mRenderTarget.CreateView()},
	mDepthTexture.CreateView());
	renderPassDesc.cDepthStencilAttachmentInfo.clearDepth = depthClear;

	// Create a render pipeline to render the quad
	utils::ComboRenderPipelineDescriptor2 renderPipelineDesc;

	renderPipelineDesc.vertex.module = vertexModule;
	renderPipelineDesc.cFragment.module = fragmentModule;
	wgpu::DepthStencilState* depthStencil = renderPipelineDesc.EnableDepthStencil(depthFormat);
	depthStencil->depthWriteEnabled = true;
	depthStencil->depthBias = bias;
	depthStencil->depthBiasSlopeScale = biasSlopeScale;
	depthStencil->depthBiasClamp = biasClamp;

	if (depthFormat != wgpu::TextureFormat::Depth32Float) {
	depthStencil->depthCompare = wgpu::CompareFunction::Greater;
	}

	wgpu::RenderPipeline pipeline = device.CreateRenderPipeline2(&renderPipelineDesc);

	// Draw the quad (two triangles)
	wgpu::CommandEncoder commandEncoder = device.CreateCommandEncoder();
	wgpu::RenderPassEncoder pass = commandEncoder.BeginRenderPass(&renderPassDesc);
	pass.SetPipeline(pipeline);
	pass.Draw(6);
	pass.EndPass();

	wgpu::CommandBuffer commands = commandEncoder.Finish();
	queue.Submit(1, &commands);
	}

	// Floating point depth buffers use the following formula to calculate bias
	// bias = depthBias * 2 ** (exponent(max z of primitive) - number of bits in mantissa) +
	// slopeScale * maxSlope
	// https://docs.microsoft.com/en-us/windows/win32/direct3d11/d3d10-graphics-programming-guide-output-merger-stage-depth-bias
	// https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/vkCmdSetDepthBias.html
	// https://developer.apple.com/documentation/metal/mtlrendercommandencoder/1516269-setdepthbias
	//
	// To get a final bias of 0.25 for primitives with z = 0.25, we can use
	// depthBias = 0.25 / (2 ** (-2 - 23)) = 8388608
	static constexpr int32_t kPointTwoFiveBiasForPointTwoFiveZOnFloat = 8388608;

	wgpu::Texture mDepthTexture;
	wgpu::Texture mRenderTarget;
	};

	// Test adding positive bias to output
	TEST_P(DepthBiasTests, PositiveBiasOnFloat) {
	// NVIDIA GPUs under Vulkan seem to be using a different scale than everyone else.
	DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

	// OpenGL uses a different scale than the other APIs
	DAWN_SKIP_TEST_IF(IsOpenGL());
	DAWN_SKIP_TEST_IF(IsOpenGLES());

	// Draw quad flat on z = 0.25 with 0.25 bias
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
	kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0);

	// Quad at z = 0.25 + 0.25 bias = 0.5
	std::vector<float> expected = {
	0.5, 0.5, //
	0.5, 0.5, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding positive bias to output with a clamp
	TEST_P(DepthBiasTests, PositiveBiasOnFloatWithClamp) {
	// Clamping support in OpenGL is spotty
	DAWN_SKIP_TEST_IF(IsOpenGL());
	DAWN_SKIP_TEST_IF(IsOpenGLES());

	// Draw quad flat on z = 0.25 with 0.25 bias clamped at 0.125.
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
	kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0.125);

	// Quad at z = 0.25 + min(0.25 bias, 0.125 clamp) = 0.375
	std::vector<float> expected = {
	0.375, 0.375, //
	0.375, 0.375, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding negative bias to output
	TEST_P(DepthBiasTests, NegativeBiasOnFloat) {
	// NVIDIA GPUs seems to be using a different scale than everyone else
	DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

	// OpenGL uses a different scale than the other APIs
	DAWN_SKIP_TEST_IF(IsOpenGL());

	// Draw quad flat on z = 0.25 with -0.25 bias, depth clear of 0.125
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::Flat,
	-kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, 0);

	// Quad at z = 0.25 - 0.25 bias = 0
	std::vector<float> expected = {
	0.0, 0.0, //
	0.0, 0.0, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding negative bias to output with a clamp
	TEST_P(DepthBiasTests, NegativeBiasOnFloatWithClamp) {
	// Clamping support in OpenGL is spotty
	DAWN_SKIP_TEST_IF(IsOpenGL());
	DAWN_SKIP_TEST_IF(IsOpenGLES());

	// Draw quad flat on z = 0.25 with -0.25 bias clamped at -0.125.
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::Flat,
	-kPointTwoFiveBiasForPointTwoFiveZOnFloat, 0, -0.125);

	// Quad at z = 0.25 + max(-0.25 bias, -0.125 clamp) = 0.125
	std::vector<float> expected = {
	0.125, 0.125, //
	0.125, 0.125, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding positive infinite slope bias to output
	TEST_P(DepthBiasTests, PositiveInfinitySlopeBiasOnFloat) {
	// NVIDIA GPUs do not clamp values to 1 when using Inf slope bias.
	DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

	// Draw quad with z from 0 to 0.5 with inf slope bias
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::TiltedX, 0,
	std::numeric_limits<float>::infinity(), 0);

	// Value at the center of the pixel + (0.25 slope * Inf slope bias) = 1 (clamped)
	std::vector<float> expected = {
	1.0, 1.0, //
	1.0, 1.0, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding positive infinite slope bias to output
	TEST_P(DepthBiasTests, NegativeInfinityBiasOnFloat) {
	// NVIDIA GPUs do not clamp values to 0 when using -Inf slope bias.
	DAWN_SKIP_TEST_IF(IsVulkan() && IsNvidia());

	// Draw quad with z from 0 to 0.5 with -inf slope bias
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0.125, QuadAngle::TiltedX, 0,
	-std::numeric_limits<float>::infinity(), 0);

	// Value at the center of the pixel + (0.25 slope * -Inf slope bias) = 0 (clamped)
	std::vector<float> expected = {
	0.0, 0.0, //
	0.0, 0.0, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test tiledX quad with no bias
	TEST_P(DepthBiasTests, NoBiasTiltedXOnFloat) {
	// Draw quad with z from 0 to 0.5 with no bias
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, 0, 0);

	// Depth values of TiltedX quad. Values at the center of the pixels.
	std::vector<float> expected = {
	0.375, 0.375, //
	0.125, 0.125, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding positive slope bias to output
	TEST_P(DepthBiasTests, PositiveSlopeBiasOnFloat) {
	// Draw quad with z from 0 to 0.5 with a slope bias of 1
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, 1, 0);

	// Value at the center of the pixel + (0.25 slope * 1.0 slope bias)
	std::vector<float> expected = {
	0.625, 0.625, //
	0.375, 0.375, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding negative half slope bias to output
	TEST_P(DepthBiasTests, NegativeHalfSlopeBiasOnFloat) {
	// Draw quad with z from 0 to 0.5 with a slope bias of -0.5
	RunDepthBiasTest(wgpu::TextureFormat::Depth32Float, 0, QuadAngle::TiltedX, 0, -0.5, 0);

	// Value at the center of the pixel + (0.25 slope * -0.5 slope bias)
	std::vector<float> expected = {
	0.25, 0.25, //
	0.0, 0.0, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mDepthTexture, {0, 0}, {kRTSize, kRTSize}, 0,
	wgpu::TextureAspect::DepthOnly);
	}

	// Test adding positive bias to output
	TEST_P(DepthBiasTests, PositiveBiasOn24bit) {
	// Draw quad flat on z = 0.25 with 0.25 bias
	RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::Flat,
	0.25f * (1 << 25), 0, 0);

	// Only the bottom left quad has colors. 0.5 quad > 0.4 clear.
	// TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
	std::vector<RGBA8> expected = {
	RGBA8::kRed, RGBA8::kRed, //
	RGBA8::kRed, RGBA8::kRed, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
	}

	// Test adding positive bias to output with a clamp
	TEST_P(DepthBiasTests, PositiveBiasOn24bitWithClamp) {
	// Clamping support in OpenGL is spotty
	DAWN_SKIP_TEST_IF(IsOpenGL());
	DAWN_SKIP_TEST_IF(IsOpenGLES());

	// Draw quad flat on z = 0.25 with 0.25 bias clamped at 0.125.
	RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::Flat,
	0.25f * (1 << 25), 0, 0.1f);

	// Since we cleared with a depth of 0.4 and clamped bias at 0.4, the depth test will fail. 0.25
	// + 0.125 < 0.4 clear.
	// TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
	std::vector<RGBA8> zero = {
	RGBA8::kZero, RGBA8::kZero, //
	RGBA8::kZero, RGBA8::kZero, //
	};

	EXPECT_TEXTURE_EQ(zero.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
	}

	// Test adding positive bias to output
	TEST_P(DepthBiasTests, PositiveSlopeBiasOn24bit) {
	// Draw quad with z from 0 to 0.5 with a slope bias of 1
	RunDepthBiasTest(wgpu::TextureFormat::Depth24PlusStencil8, 0.4f, QuadAngle::TiltedX, 0, 1, 0);

	// Only the top half of the quad has a depth > 0.4 clear
	// TODO(enrico.galli@intel.com): Switch to depth sampling once feature has been enabled.
	std::vector<RGBA8> expected = {
	RGBA8::kRed, RGBA8::kRed, //
	RGBA8::kZero, RGBA8::kZero, //
	};

	EXPECT_TEXTURE_EQ(expected.data(), mRenderTarget, {0, 0}, {kRTSize, kRTSize});
	}

	DAWN_INSTANTIATE_TEST(DepthBiasTests,
	D3D12Backend(),
	MetalBackend(),
	OpenGLBackend(),
	OpenGLESBackend(),
	VulkanBackend());