shell/platform/windows/compositor_opengl.cc

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "flutter/shell/platform/windows/compositor_opengl.h"

#include "GLES3/gl3.h"
#include "flutter/shell/platform/windows/flutter_windows_engine.h"
#include "flutter/shell/platform/windows/flutter_windows_view.h"

namespace flutter {

namespace {

constexpr uint32_t kWindowFrameBufferId = 0;

// The metadata for an OpenGL framebuffer backing store.
struct FramebufferBackingStore {
  uint32_t framebuffer_id;
  uint32_t texture_id;
};

// Based off Skia's logic:
// https://github.com/google/skia/blob/4738ed711e03212aceec3cd502a4adb545f38e63/src/gpu/ganesh/gl/GrGLCaps.cpp#L1963-L2116
int GetSupportedTextureFormat(const impeller::DescriptionGLES* description) {
  if (description->HasExtension("GL_EXT_texture_format_BGRA8888")) {
    return GL_BGRA8_EXT;
  } else if (description->HasExtension("GL_APPLE_texture_format_BGRA8888") &&
             description->GetGlVersion().IsAtLeast(impeller::Version(3, 0))) {
    return GL_BGRA8_EXT;
  } else {
    return GL_RGBA8;
  }
}

}  // namespace

CompositorOpenGL::CompositorOpenGL(FlutterWindowsEngine* engine,
                                   impeller::ProcTableGLES::Resolver resolver)
    : engine_(engine), resolver_(resolver) {}

bool CompositorOpenGL::CreateBackingStore(
    const FlutterBackingStoreConfig& config,
    FlutterBackingStore* result) {
  if (!is_initialized_ && !Initialize()) {
    return false;
  }

  auto store = std::make_unique<FramebufferBackingStore>();

  gl_->GenTextures(1, &store->texture_id);
  gl_->GenFramebuffers(1, &store->framebuffer_id);

  gl_->BindFramebuffer(GL_FRAMEBUFFER, store->framebuffer_id);

  gl_->BindTexture(GL_TEXTURE_2D, store->texture_id);
  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
  gl_->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
  gl_->TexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, config.size.width,
                  config.size.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
  gl_->BindTexture(GL_TEXTURE_2D, 0);

  gl_->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0_EXT,
                            GL_TEXTURE_2D, store->texture_id, 0);

  result->type = kFlutterBackingStoreTypeOpenGL;
  result->open_gl.type = kFlutterOpenGLTargetTypeFramebuffer;
  result->open_gl.framebuffer.name = store->framebuffer_id;
  result->open_gl.framebuffer.target = format_;
  result->open_gl.framebuffer.user_data = store.release();
  result->open_gl.framebuffer.destruction_callback = [](void* user_data) {
    // Backing store destroyed in `CompositorOpenGL::CollectBackingStore`, set
    // on FlutterCompositor.collect_backing_store_callback during engine start.
  };
  return true;
}

bool CompositorOpenGL::CollectBackingStore(const FlutterBackingStore* store) {
  FML_DCHECK(is_initialized_);
  FML_DCHECK(store->type == kFlutterBackingStoreTypeOpenGL);
  FML_DCHECK(store->open_gl.type == kFlutterOpenGLTargetTypeFramebuffer);

  auto user_data = static_cast<FramebufferBackingStore*>(
      store->open_gl.framebuffer.user_data);

  gl_->DeleteFramebuffers(1, &user_data->framebuffer_id);
  gl_->DeleteTextures(1, &user_data->texture_id);

  delete user_data;
  return true;
}

bool CompositorOpenGL::Present(FlutterViewId view_id,
                               const FlutterLayer** layers,
                               size_t layers_count) {
  FlutterWindowsView* view = engine_->view(view_id);
  if (!view) {
    return false;
  }

  // Clear the view if there are no layers to present.
  if (layers_count == 0) {
    // Normally the compositor is initialized when the first backing store is
    // created. However, on an empty frame no backing stores are created and
    // the present needs to initialize the compositor.
    if (!is_initialized_ && !Initialize()) {
      return false;
    }

    return Clear(view);
  }

  // TODO: Support compositing layers and platform views.
  // See: https://github.com/flutter/flutter/issues/31713
  FML_DCHECK(is_initialized_);
  FML_DCHECK(layers_count == 1);
  FML_DCHECK(layers[0]->offset.x == 0 && layers[0]->offset.y == 0);
  FML_DCHECK(layers[0]->type == kFlutterLayerContentTypeBackingStore);
  FML_DCHECK(layers[0]->backing_store->type == kFlutterBackingStoreTypeOpenGL);
  FML_DCHECK(layers[0]->backing_store->open_gl.type ==
             kFlutterOpenGLTargetTypeFramebuffer);

  auto width = layers[0]->size.width;
  auto height = layers[0]->size.height;

  // Check if this frame can be presented. This resizes the surface if a resize
  // is pending and |width| and |height| match the target size.
  if (!view->OnFrameGenerated(width, height)) {
    return false;
  }

  // |OnFrameGenerated| should return false if the surface isn't valid.
  FML_DCHECK(view->surface() != nullptr);
  FML_DCHECK(view->surface()->IsValid());

  egl::WindowSurface* surface = view->surface();
  if (!surface->MakeCurrent()) {
    return false;
  }

  auto source_id = layers[0]->backing_store->open_gl.framebuffer.name;

  // Disable the scissor test as it can affect blit operations.
  // Prevents regressions like: https://github.com/flutter/flutter/issues/140828
  // See OpenGL specification version 4.6, section 18.3.1.
  gl_->Disable(GL_SCISSOR_TEST);

  gl_->BindFramebuffer(GL_READ_FRAMEBUFFER, source_id);
  gl_->BindFramebuffer(GL_DRAW_FRAMEBUFFER, kWindowFrameBufferId);

  gl_->BlitFramebuffer(0,                    // srcX0
                       0,                    // srcY0
                       width,                // srcX1
                       height,               // srcY1
                       0,                    // dstX0
                       0,                    // dstY0
                       width,                // dstX1
                       height,               // dstY1
                       GL_COLOR_BUFFER_BIT,  // mask
                       GL_NEAREST            // filter
  );

  if (!surface->SwapBuffers()) {
    return false;
  }

  view->OnFramePresented();
  return true;
}

bool CompositorOpenGL::Initialize() {
  FML_DCHECK(!is_initialized_);

  egl::Manager* manager = engine_->egl_manager();
  if (!manager) {
    return false;
  }

  if (!manager->render_context()->MakeCurrent()) {
    return false;
  }

  gl_ = std::make_unique<impeller::ProcTableGLES>(resolver_);
  if (!gl_->IsValid()) {
    gl_.reset();
    return false;
  }

  format_ = GetSupportedTextureFormat(gl_->GetDescription());
  is_initialized_ = true;
  return true;
}

bool CompositorOpenGL::Clear(FlutterWindowsView* view) {
  FML_DCHECK(is_initialized_);

  // Check if this frame can be presented. This resizes the surface if needed.
  if (!view->OnEmptyFrameGenerated()) {
    return false;
  }

  // |OnEmptyFrameGenerated| should return false if the surface isn't valid.
  FML_DCHECK(view->surface() != nullptr);
  FML_DCHECK(view->surface()->IsValid());

  egl::WindowSurface* surface = view->surface();
  if (!surface->MakeCurrent()) {
    return false;
  }

  gl_->ClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  gl_->Clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

  if (!surface->SwapBuffers()) {
    return false;
  }

  view->OnFramePresented();
  return true;
}

}  // namespace flutter