Fix incorrect texture format with OpenGL ES

shell/platform/linux/fl_backing_store_provider.cc

@@ -77,7 +77,31 @@ uint32_t fl_backing_store_provider_get_gl_target(FlBackingStoreProvider* self) {
   return GL_TEXTURE_2D;
 }
 
+static int gl_version(uint32_t major, uint32_t minor) {
+  return (major << 16) | minor;
+}
+
 uint32_t fl_backing_store_provider_get_gl_format(FlBackingStoreProvider* self) {
+  // Flutter defines SK_R32_SHIFT=16, so SK_PMCOLOR_BYTE_ORDER should be BGRA.
+  // In Linux kN32_SkColorType is assumed to be kBGRA_8888_SkColorType.
+  // So we must choose a valid gl format to be compatible with surface format
+  // BGRA8.
+  // Following logics are copied from Skia GrGLCaps.cpp
+
+  if (epoxy_is_desktop_gl()) {
+    if (epoxy_gl_version() >= gl_version(1, 2) ||
+        epoxy_has_gl_extension("GL_EXT_bgra")) {
+      return GL_RGBA8;
+    }
+  } else {
+    // For OpenGL ES.
+    if (epoxy_has_gl_extension("GL_EXT_texture_format_BGRA8888") ||
+        (epoxy_has_gl_extension("GL_APPLE_texture_format_BGRA8888") &&
+         epoxy_gl_version() >= gl_version(3, 0))) {
+      return GL_BGRA8_EXT;
+    }
+  }
+  g_critical("Failed to determine valid GL format for Flutter rendering");
   return GL_RGBA8;
 }
 

shell/platform/linux/testing/mock_epoxy.cc

@@ -374,6 +374,18 @@ static void _glTexImage2D(GLenum target,
                           GLenum type,
                           const void* pixels) {}
 
+bool epoxy_has_gl_extension(const char* extension) {
+  return false;
+}
+
+bool epoxy_is_desktop_gl(void) {
+  return false;
+}
+
+int epoxy_gl_version(void) {
+  return 0;
+}
+
 #ifdef __GNUC__
 #define CONSTRUCT(_func) static void _func(void) __attribute__((constructor));
 #define DESTRUCT(_func) static void _func(void) __attribute__((destructor));