Partial repaint prototype.

examples/glfw/FlutterEmbedderGLFW.cc

@@ -96,8 +96,16 @@ bool RunFlutter(GLFWwindow* window,
     glfwMakeContextCurrent(nullptr);  // is this even a thing?
     return true;
   };
-  config.open_gl.present = [](void* userdata) -> bool {
-    glfwSwapBuffers(static_cast<GLFWwindow*>(userdata));
+  config.open_gl.present_with_info = [](void* userdata, FlutterPresentInfo* present_info) -> bool {
+    // Check if damage exists
+    if (present_info->fbo_damage.empty()) {
+      // Render only damaged regions
+      // TODO(btrevisan): verify extensions.
+      eglSwapBuffersWithDamageKHR(static_cast<GLFWwindow*>(userdata), present_info->fbo_damage);
+    } else {
+      // Otherwise, render the entire screen
+      glfwSwapBuffers(static_cast<GLFWwindow*>(userdata));
+    }
     return true;
   };
   config.open_gl.fbo_callback = [](void*) -> uint32_t {

shell/gpu/gpu_surface_gl_delegate.cc

@@ -20,6 +20,12 @@ SurfaceFrame::FramebufferInfo GPUSurfaceGLDelegate::GLContextFramebufferInfo()
     const {
   SurfaceFrame::FramebufferInfo res;
   res.supports_readback = true;
+  // By default, partial repaint is enabled for every frame.
+  // TODO(btrevisan): Implement deactivation of partial repaint in  cases that
+  // do not benefit from it (e.g. when damage takes over most of the frame).
+  res.supports_partial_repaint = true;
+  // TODO(btrevisan): make sure that when there is existing damage, it is set.
+  res.existing_damage = SkIRect::MakeEmpty();
   return res;
 }
 

shell/gpu/gpu_surface_gl_skia.cc

@@ -248,6 +248,10 @@ std::unique_ptr<SurfaceFrame> GPUSurfaceGLSkia::AcquireFrame(
       };
 
   framebuffer_info = delegate_->GLContextFramebufferInfo();
+  // CHECK IF PARTIAL REPAINT IS ENABLED
+    // CALCULATE ACCUMULATED DAMAGE (I.E. ARE IN CURRENT FBO THAT LAGS BEHIND FRONT BUFFER)
+    // SET ACCUMULATED DAMAGE TO FBO_INFO EXISTING_DAMAGE
+    // SET SUPPORTS_PARTIAL_REPAINT TO TRUE
   return std::make_unique<SurfaceFrame>(surface, std::move(framebuffer_info),
                                         submit_callback,
                                         std::move(context_switch));

shell/platform/embedder/embedder.cc

@@ -240,15 +240,25 @@ InferOpenGLPlatformViewCreationCallback(
   auto gl_clear_current = [ptr = config->open_gl.clear_current,
                            user_data]() -> bool { return ptr(user_data); };
 
-  auto gl_present = [present = config->open_gl.present,
-                     present_with_info = config->open_gl.present_with_info,
-                     user_data](uint32_t fbo_id) -> bool {
+  auto gl_present =
+      [present = config->open_gl.present,
+       present_with_info = config->open_gl.present_with_info,
+       user_data](flutter::GLPresentInfo gl_present_info) -> bool {
     if (present) {
       return present(user_data);
     } else {
       FlutterPresentInfo present_info = {};
       present_info.struct_size = sizeof(FlutterPresentInfo);
-      present_info.fbo_id = fbo_id;
+      present_info.fbo_id = gl_present_info.fbo_id;
+
+      FlutterDamage fbo_damage = {};
+      fbo_damage.struct_size = sizeof(FlutterDamage);
+      fbo_damage.damage = std::vector<FlutterRect>{
+          FlutterRect{static_cast<double>(gl_present_info.damage->fLeft),
+                      static_cast<double>(gl_present_info.damage->fRight),
+                      static_cast<double>(gl_present_info.damage->fTop),
+                      static_cast<double>(gl_present_info.damage->fBottom)}};
+      present_info.fbo_damage = fbo_damage;
       return present_with_info(user_data, &present_info);
     }
   };

shell/platform/embedder/embedder.h

@@ -8,6 +8,7 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <vector>
 
 // This file defines an Application Binary Interface (ABI), which requires more
 // stability than regular code to remain functional for exchanging messages
@@ -377,6 +378,14 @@ typedef struct {
   FlutterSize lower_left_corner_radius;
 } FlutterRoundedRect;
 
+/// A strucutre to represent damage as rectangles.
+typedef struct {
+  /// The size of this struct. Must be sizeof(FlutterDamage).
+  size_t struct_size;
+  // Vector of rectangles representing the areas that need to be repainted.
+  std::vector<FlutterRect> damage;
+} FlutterDamage;
+
 /// This information is passed to the embedder when requesting a frame buffer
 /// object.
 ///
@@ -401,6 +410,8 @@ typedef struct {
   size_t struct_size;
   /// Id of the fbo backing the surface that was presented.
   uint32_t fbo_id;
+  // A vector of rectangles representing the areas that need to be repainted.
+  FlutterDamage fbo_damage;
 } FlutterPresentInfo;
 
 /// Callback for when a surface is presented.

shell/platform/embedder/embedder_surface_gl.cc

@@ -24,6 +24,11 @@ EmbedderSurfaceGL::EmbedderSurfaceGL(
   }
 
   valid_ = true;
+
+  // if (HasExtension(extensions, "EGL_KHR_partial_update")) {
+  //   set_damage_region_ = reinterpret_cast<PFNEGLSETDAMAGEREGIONKHRPROC>(
+  //       eglGetProcAddress("eglSetDamageRegionKHR"));
+  // }
 }
 
 EmbedderSurfaceGL::~EmbedderSurfaceGL() = default;
@@ -46,7 +51,7 @@ bool EmbedderSurfaceGL::GLContextClearCurrent() {
 
 // |GPUSurfaceGLDelegate|
 bool EmbedderSurfaceGL::GLContextPresent(const GLPresentInfo& present_info) {
-  return gl_dispatch_table_.gl_present_callback(present_info.fbo_id);
+  return gl_dispatch_table_.gl_present_callback(present_info);
 }
 
 // |GPUSurfaceGLDelegate|
@@ -59,6 +64,16 @@ bool EmbedderSurfaceGL::GLContextFBOResetAfterPresent() const {
   return fbo_reset_after_present_;
 }
 
+// |GPUSurfaceGLDelegate|
+void EmbedderSurfaceGL::GLContextSetDamageRegion(
+    const std::optional<SkIRect>& region) {
+  // TODO(btrevisan): add checks.
+  FML_DCHECK(IsValid());
+
+  // The region given here is the buffer damage.
+  // onscreen_surface_->SetDamageRegion(region);
+}
+
 // |GPUSurfaceGLDelegate|
 SkMatrix EmbedderSurfaceGL::GLContextSurfaceTransformation() const {
   auto callback = gl_dispatch_table_.gl_surface_transformation_callback;

shell/platform/embedder/embedder_surface_gl.h

@@ -18,7 +18,7 @@ class EmbedderSurfaceGL final : public EmbedderSurface,
   struct GLDispatchTable {
     std::function<bool(void)> gl_make_current_callback;           // required
     std::function<bool(void)> gl_clear_current_callback;          // required
-    std::function<bool(uint32_t)> gl_present_callback;            // required
+    std::function<bool(GLPresentInfo)> gl_present_callback;       // required
     std::function<intptr_t(GLFrameInfo)> gl_fbo_callback;         // required
     std::function<bool(void)> gl_make_resource_current_callback;  // optional
     std::function<SkMatrix(void)>
@@ -37,6 +37,7 @@ class EmbedderSurfaceGL final : public EmbedderSurface,
   bool valid_ = false;
   GLDispatchTable gl_dispatch_table_;
   bool fbo_reset_after_present_;
+  // auto set_damage_region_ = nullptr;
 
   std::shared_ptr<EmbedderExternalViewEmbedder> external_view_embedder_;
 
@@ -64,6 +65,9 @@ class EmbedderSurfaceGL final : public EmbedderSurface,
   // |GPUSurfaceGLDelegate|
   bool GLContextFBOResetAfterPresent() const override;
 
+  // |GPUSurfaceGLDelegate|
+  void GLContextSetDamageRegion(const std::optional<SkIRect>& region) override;
+
   // |GPUSurfaceGLDelegate|
   SkMatrix GLContextSurfaceTransformation() const override;