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Honor the surface's alphaMode on the Vulkan swapchain #69

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Honor the surface's alphaMode on the Vulkan swapchain #69

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40 changes: 20 additions & 20 deletions src/dawn/native/vulkan/SwapChainVk.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,6 @@
#include <utility>

#include "src/dawn/common/Compiler.h"
#include "src/dawn/common/Range.h"
#include "src/dawn/native/ChainUtils.h"
#include "src/dawn/native/Instance.h"
#include "src/dawn/native/Surface.h"
Expand Down Expand Up @@ -296,33 +295,34 @@ ResultOrError<SwapChain::Config> SwapChain::ChooseConfig(
"Vulkan SwapChain must support %s with sRGB colorspace.", config.wgpuFormat));
}

// Only the identity transform with opaque alpha is supported for now.
// Only the identity transform is supported for now.
DAWN_INVALID_IF(
(surfaceInfo.capabilities.supportedTransforms & VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR) == 0,
"Vulkan SwapChain must support the identity transform.");

config.transform = VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR;

config.alphaMode = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
#if !DAWN_PLATFORM_IS(ANDROID)
DAWN_INVALID_IF(
(surfaceInfo.capabilities.supportedCompositeAlpha & VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR) == 0,
"Vulkan SwapChain must support opaque alpha.");
#else
// TODO(dawn:286): investigate composite alpha for WebGPU native
std::array<VkCompositeAlphaFlagBitsKHR, 4u> compositeAlphaFlags = {
VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR,
VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR,
VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR,
};
for (uint32_t i : Range(4u)) {
if (surfaceInfo.capabilities.supportedCompositeAlpha & compositeAlphaFlags[i]) {
config.alphaMode = compositeAlphaFlags[i];
// Choose the Vulkan alpha mode by directly converting from the WebGPU enum. PhysicalDeviceVk
// only reports the alpha modes the surface supports, Surface.cpp resolves Auto and validates
// the rest, so the mode asked for here is always available.
switch (GetAlphaMode()) {
case wgpu::CompositeAlphaMode::Opaque:
config.alphaMode = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
break;
}
case wgpu::CompositeAlphaMode::Premultiplied:
config.alphaMode = VK_COMPOSITE_ALPHA_PRE_MULTIPLIED_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Unpremultiplied:
config.alphaMode = VK_COMPOSITE_ALPHA_POST_MULTIPLIED_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Inherit:
config.alphaMode = VK_COMPOSITE_ALPHA_INHERIT_BIT_KHR;
break;
case wgpu::CompositeAlphaMode::Auto:
default:
DAWN_UNREACHABLE();
}
#endif // #if !DAWN_PLATFORM_IS(ANDROID)
DAWN_CHECK((surfaceInfo.capabilities.supportedCompositeAlpha & config.alphaMode) != 0);

// Choose the number of images for the swapchain= and clamp it to the min and max from the
// surface capabilities. maxImageCount = 0 means there is no limit.
Expand Down
22 changes: 18 additions & 4 deletions src/dawn/samples/ManualSurfaceTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
// This is an example to manually test surface code. Controls are the following, scoped to the
// currently focused window:
// - W: creates a new window.
// - T: creates a new window with a transparent framebuffer, to test the alpha modes.
// - L: Latches the current surface, to check what happens when the window changes but not the
// surface.
// - R: switches the rendering mode, between "The Red Triangle" and color-cycling clears that's
Expand Down Expand Up @@ -64,6 +65,9 @@
// - Config change tests:
// - Check that cycling between present modes.
// - Check that cycling between alpha modes (it sometimes produce a meaningful difference).
// - Check alpha modes on a transparent window (T) in the cycling color render mode: the clear
// is premultiplied and cycles its alpha, so Premultiplied and Unpremultiplied let the
// desktop show through and Opaque does not.
// - Check that cycling between formats works and gives the same color.
//
// - Frame throttling:
Expand All @@ -75,7 +79,6 @@
// - Check sRGB vs not sRGB gradients.
// - Check wide gamut / extended color range.
// - Check OpenGL rendering with extra usages / depth buffer / MRT.
// - Check with GLFW transparency on / off.

#include <webgpu/webgpu_cpp.h>

Expand Down Expand Up @@ -125,6 +128,7 @@ struct WindowData {
uint64_t serial = 0;

float clearCycle = 1.0f;
bool transparent = false;
bool latched = false;
bool renderTriangle = true;
uint32_t divisor = 1;
Expand Down Expand Up @@ -200,8 +204,9 @@ void SyncFromWindow(WindowData* data) {
data->targetConfig.height = std::max(1u, static_cast<uint32_t>(height) / data->divisor);
}

void AddWindow() {
void AddWindow(bool transparent = false) {
glfwWindowHint(GLFW_CLIENT_API, GLFW_NO_API);
glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, transparent ? GLFW_TRUE : GLFW_FALSE);
GLFWwindow* window = glfwCreateWindow(400, 400, "", nullptr, nullptr);
glfwSetKeyCallback(window, OnKeyPress);

Expand All @@ -221,6 +226,7 @@ void AddWindow() {
std::unique_ptr<WindowData> data = std::make_unique<WindowData>();
data->window = window;
data->serial = windowSerial++;
data->transparent = transparent;
data->surface = surface;
data->currentConfig = config;
data->targetConfig = config;
Expand Down Expand Up @@ -257,10 +263,14 @@ void DoRender(WindowData* data) {
data->clearCycle = 1.0f;
}

// On a transparent window cycle the alpha as well, so that the alpha modes have a
// visible effect. The color channels are premultiplied so that Premultiplied is valid.
const double alpha = data->transparent ? double{data->clearCycle} : 1.0;

dawn::utils::ComboRenderPassDescriptor desc({view});
desc.cColorAttachments[0].loadOp = wgpu::LoadOp::Clear;
desc.cColorAttachments[0].clearValue = {double{data->clearCycle},
double{1.0f - data->clearCycle}, 0.0, 1.0};
desc.cColorAttachments[0].clearValue = {
alpha * double{data->clearCycle}, alpha * double{1.0f - data->clearCycle}, 0.0, alpha};

wgpu::RenderPassEncoder pass = encoder.BeginRenderPass(&desc);
pass.End();
Expand Down Expand Up @@ -316,6 +326,10 @@ void OnKeyPress(GLFWwindow* window, int key, int, int action, int) {
AddWindow();
break;

case GLFW_KEY_T:
AddWindow(/*transparent=*/true);
break;

case GLFW_KEY_L:
data->latched = !data->latched;
UpdateTitle(data);
Expand Down