Add WebGPU Backend w/ Dawn Support (#3838)

include/mbgl/shaders/webgpu/debug.hpp

@@ -0,0 +1,80 @@
+#pragma once
+
+#include <mbgl/shaders/debug_layer_ubo.hpp>
+#include <mbgl/shaders/shader_source.hpp>
+#include <mbgl/shaders/webgpu/shader_program.hpp>
+
+namespace mbgl {
+namespace shaders {
+
+template <>
+struct ShaderSource<BuiltIn::DebugShader, gfx::Backend::Type::WebGPU> {
+    static constexpr const char* name = "DebugShader";
+    static const std::array<AttributeInfo, 1> attributes;
+    static constexpr std::array<AttributeInfo, 0> instanceAttributes{};
+    static const std::array<TextureInfo, 1> textures;
+
+    static constexpr auto vertex = R"(
+struct VertexInput {
+    @location(5) position: vec2<i32>,
+};
+
+struct VertexOutput {
+    @builtin(position) position: vec4<f32>,
+    @location(0) uv: vec2<f32>,
+};
+
+struct DebugUBO {
+    matrix: mat4x4<f32>,
+    color: vec4<f32>,
+    overlay_scale: f32,
+    pad1: f32,
+    pad2: f32,
+    pad3: f32,
+};
+
+@group(0) @binding(0) var<uniform> debug: DebugUBO;
+
+@vertex
+fn main(in: VertexInput) -> VertexOutput {
+    var out: VertexOutput;
+
+    let scaled_pos = vec2<f32>(f32(in.position.x), f32(in.position.y)) * debug.overlay_scale;
+    out.position = debug.matrix * vec4<f32>(scaled_pos, 0.0, 1.0);
+
+    // This vertex shader expects a EXTENT x EXTENT quad,
+    // The UV co-ordinates for the overlay texture can be calculated using that knowledge
+    out.uv = vec2<f32>(f32(in.position.x), f32(in.position.y)) / 8192.0;
+
+    return out;
+}
+)";
+
+    static constexpr auto fragment = R"(
+struct FragmentInput {
+    @location(0) uv: vec2<f32>,
+};
+
+struct DebugUBO {
+    matrix: mat4x4<f32>,
+    color: vec4<f32>,
+    overlay_scale: f32,
+    pad1: f32,
+    pad2: f32,
+    pad3: f32,
+};
+
+@group(0) @binding(0) var<uniform> debug: DebugUBO;
+@group(1) @binding(0) var texture_sampler: sampler;
+@group(1) @binding(1) var overlay_texture: texture_2d<f32>;
+
+@fragment
+fn main(in: FragmentInput) -> @location(0) vec4<f32> {
+    let overlay_color = textureSample(overlay_texture, texture_sampler, in.uv);
+    return mix(debug.color, overlay_color, overlay_color.a);
+}
+)";
+};
+
+} // namespace shaders
+} // namespace mbgl