Add WebGPU Backend w/ Dawn Support (#3838)

src/mbgl/webgpu/drawable_builder.cpp

@@ -0,0 +1,88 @@
+#include <mbgl/webgpu/drawable_builder.hpp>
+#include <mbgl/gfx/drawable_builder_impl.hpp>
+#include <mbgl/gfx/drawable_impl.hpp>
+#include <mbgl/webgpu/drawable.hpp>
+#include <mbgl/webgpu/drawable_impl.hpp>
+#include <mbgl/webgpu/context.hpp>
+#include <mbgl/util/logging.hpp>
+
+namespace mbgl {
+namespace webgpu {
+
+DrawableBuilder::DrawableBuilder(std::string name_)
+    : gfx::DrawableBuilder(std::move(name_)) {}
+
+DrawableBuilder::~DrawableBuilder() = default;
+
+std::unique_ptr<gfx::Drawable> DrawableBuilder::createDrawable() const {
+    return std::make_unique<Drawable>(name);
+}
+
+std::unique_ptr<gfx::Drawable::DrawSegment> DrawableBuilder::createSegment(gfx::DrawMode drawMode,
+                                                                           SegmentBase&& segment) {
+    return std::make_unique<Drawable::DrawSegment>(drawMode, std::move(segment));
+}
+
+void DrawableBuilder::init() {
+    if (!currentDrawable) {
+        mbgl::Log::Warning(mbgl::Event::Render, "DrawableBuilder::init called with no current drawable");
+        return;
+    }
+
+    auto& drawable = static_cast<Drawable&>(*currentDrawable);
+
+    // Set the vertex attribute ID so the drawable knows which shared vertex buffer to use
+    drawable.setVertexAttrId(vertexAttrId);
+
+    // Handle special case where rawVerticesCount is set but rawVertices is empty (from fills)
+    // In this case, the vertex data is in the vertex attributes
+    if (impl->rawVerticesCount && impl->rawVertices.empty()) {
+        // The vertex data is in the vertex attributes, use updateVertexAttributes
+        // Get the vertex attributes from the drawable (already set by base class flush())
+        if (drawable.getVertexAttributes() && !impl->segments.empty()) {
+            // Get the draw mode from the first segment
+            gfx::DrawMode drawMode = impl->segments[0]->getMode();
+            // The segments in the drawable will be set by setIndexData below
+            // We just need to trigger the vertex attribute extraction
+            // Pass empty segments for now since setIndexData will set them properly
+            drawable.updateVertexAttributes(
+                drawable.getVertexAttributes(), impl->rawVerticesCount, drawMode, impl->sharedIndexes, nullptr, 0);
+
+        } else {
+        }
+    } else if (impl->rawVerticesCount && !impl->rawVertices.empty()) {
+        auto raw = std::move(impl->rawVertices);
+        drawable.setVertices(std::move(raw), impl->rawVerticesCount, impl->rawVerticesType);
+    } else if (!impl->vertices.empty()) {
+        const auto& verts = impl->vertices.vector();
+
+        if (!verts.empty()) {
+            constexpr auto vertSize = sizeof(std::remove_reference<decltype(verts)>::type::value_type);
+            std::vector<uint8_t> raw(verts.size() * vertSize);
+            std::memcpy(raw.data(), verts.data(), raw.size());
+            drawable.setVertices(std::move(raw), verts.size(), gfx::AttributeDataType::Short2);
+        }
+    } else {
+    }
+
+    // Set index data if available
+    if (!impl->sharedIndexes && !impl->buildIndexes.empty()) {
+        impl->sharedIndexes = std::make_shared<gfx::IndexVectorBase>(std::move(impl->buildIndexes));
+    }
+
+    if (impl->sharedIndexes && impl->sharedIndexes->elements()) {
+        drawable.setIndexData(impl->sharedIndexes, std::move(impl->segments));
+    } else {
+        mbgl::Log::Warning(mbgl::Event::Render, "  No index data to set!");
+    }
+
+    // Flush texture bindings so the shared builder doesn't leak the previous tile's
+    // Texture2D handles into the next draw call. Other backends reset textures while
+    // binding state; WebGPU relies on the builder being fresh per pass.
+    for (auto& textureSlot : textures) {
+        textureSlot.reset();
+    }
+}
+
+} // namespace webgpu
+} // namespace mbgl