Fix transparent viewport backgrounds with custom clear color

(cherry picked from commit 6effd3cde7a481b57226cf5d03c97aa5728ff7e7)

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -1734,7 +1734,7 @@ void RasterizerSceneGLES3::render_scene(const Ref<RenderSceneBuffers> &p_render_
 	RenderDataGLES3 render_data;
 	{
 		render_data.render_buffers = rb;
-		render_data.transparent_bg = rb.is_valid() ? rb->is_transparent : false;
+		render_data.transparent_bg = rb.is_valid() ? rt->is_transparent : false;
 		// Our first camera is used by default
 		render_data.cam_transform = p_camera_data->main_transform;
 		render_data.inv_cam_transform = render_data.cam_transform.affine_inverse();
@@ -1980,6 +1980,7 @@ void RasterizerSceneGLES3::render_scene(const Ref<RenderSceneBuffers> &p_render_
 	}
 
 	if (!keep_color) {
+		clear_color.a = render_data.transparent_bg ? 0.0f : 1.0f;
 		glClearBufferfv(GL_COLOR, 0, clear_color.components);
 	}
 	RENDER_TIMESTAMP("Render Opaque Pass");

drivers/gles3/storage/render_scene_buffers_gles3.cpp

@@ -38,8 +38,6 @@ RenderSceneBuffersGLES3::~RenderSceneBuffersGLES3() {
 }
 
 void RenderSceneBuffersGLES3::configure(RID p_render_target, const Size2i p_internal_size, const Size2i p_target_size, RS::ViewportScaling3DMode p_scaling_3d_mode, float p_fsr_sharpness, float p_texture_mipmap_bias, RS::ViewportMSAA p_msaa, RenderingServer::ViewportScreenSpaceAA p_screen_space_aa, bool p_use_taa, bool p_use_debanding, uint32_t p_view_count) {
-	GLES3::TextureStorage *texture_storage = GLES3::TextureStorage::get_singleton();
-
 	//internal_size.x = p_internal_size.x; // ignore for now
 	//internal_size.y = p_internal_size.y;
 	width = p_target_size.x;
@@ -54,10 +52,6 @@ void RenderSceneBuffersGLES3::configure(RID p_render_target, const Size2i p_inte
 	view_count = p_view_count;
 
 	free_render_buffer_data();
-
-	GLES3::RenderTarget *rt = texture_storage->get_render_target(p_render_target);
-
-	is_transparent = rt->is_transparent;
 }
 
 void RenderSceneBuffersGLES3::free_render_buffer_data() {

drivers/gles3/storage/render_scene_buffers_gles3.h

@@ -58,8 +58,6 @@ public:
 	//bool use_debanding = false;
 	uint32_t view_count = 1;
 
-	bool is_transparent = false;
-
 	RID render_target;
 
 	//built-in textures used for ping pong image processing and blurring

servers/rendering/renderer_rd/forward_mobile/render_forward_mobile.cpp

@@ -921,13 +921,19 @@ void RenderForwardMobile::_render_scene(RenderDataRD *p_render_data, const Color
 		{
 			// regular forward for now
 			Vector<Color> c;
-			c.push_back(clear_color.srgb_to_linear()); // our render buffer
-			if (rb_data.is_valid()) {
-				if (p_render_data->render_buffers->get_msaa_3d() != RS::VIEWPORT_MSAA_DISABLED) {
-					c.push_back(clear_color.srgb_to_linear()); // our resolve buffer
+			{
+				Color cc = clear_color.srgb_to_linear();
+				if (rb_data.is_valid()) {
+					cc.a = 0; // For transparent viewport backgrounds.
 				}
-				if (using_subpass_post_process) {
-					c.push_back(Color()); // our 2D buffer we're copying into
+				c.push_back(cc); // Our render buffer.
+				if (rb_data.is_valid()) {
+					if (p_render_data->render_buffers->get_msaa_3d() != RS::VIEWPORT_MSAA_DISABLED) {
+						c.push_back(clear_color.srgb_to_linear()); // Our resolve buffer.
+					}
+					if (using_subpass_post_process) {
+						c.push_back(Color()); // Our 2D buffer we're copying into.
+					}
 				}
 			}