GLES3 not working on android emulator + workaround

[ChibiDenDen]

Godot version

9b9bb41

System information

Android12 emulator, GLES3

Issue description

Using Godot 4 on an Android emulator with the GLES3 renderer results in a black screen and no crash / erros.

I managed to resolve the issue with the following change:

--- a/drivers/gles3/storage/texture_storage.cpp
+++ b/drivers/gles3/storage/texture_storage.cpp
@@ -1599,9 +1599,9 @@ void TextureStorage::_update_render_target(RenderTarget *rt) {
 
        Config *config = Config::get_singleton();
 
-       rt->color_internal_format = rt->is_transparent ? GL_RGBA8 : GL_RGB10_A2;
+       rt->color_internal_format = rt->is_transparent ? GL_RGBA8 : GL_RGBA8;
        rt->color_format = GL_RGBA;
-       rt->color_type = rt->is_transparent ? GL_UNSIGNED_BYTE : GL_UNSIGNED_INT_2_10_10_10_REV;
+       rt->color_type = rt->is_transparent ? GL_UNSIGNED_BYTE : GL_UNSIGNED_BYTE;
        rt->image_format = Image::FORMAT_RGBA8;

Which effectively disables the RGB10_A2 internal format for render targets and uses RGBA8 instead.
These 2 format changes fix rendering on my android emulator.

Im not sure what RGB10_A2 is used for (HDR?), but my workaround does not seem like the best solution.

Perhaps someone who knows a little bit more about the code here could suggest a different solution.

Steps to reproduce

Run any godot project on android emulator using GLES3 renderer.

Might be relevant:
my host machine is an M1 macbook pro

Minimal reproduction project

N/A

[clayjohn]

It sounds like your emulator doesn't fully support OpenGL ES 3.0. Being able to render to a GL_RGB10_A2 render target is a core requirement for a device to claim OpenGL ES 3.0 support.

[ChibiDenDen]

I absolutely agree, but I was wondering if I'm missing something else and the format is not really the issue...

I looked for a way to check if a format is supported but like you said, it is assumed to work on all gles3 devices.
The framebuffer is even claimed to be complete and no command results in any glError in this method..

Some questions that come to mind:
Is there anything else you think that might cause this issue?
Does changing the format has any other effect?
Why is 10_A2 used here? Is it for HDR?

For reference, I'm using the standard emulator in Android studio.

[clayjohn]

Is there anything else you think that might cause this issue?
Does changing the format has any other effect?

I can't think of anything else that would be responsible that would also go away when switching to an RGBA8 buffer.

Why is 10_A2 used here? Is it for HDR?

It's used to reduce banding in 3D. 8bits is really low precision for 3D rendering. Using 10 bits helps a lot

[ChibiDenDen]

I played with it a bit more and found out another way to "solve" the issue without disabling RGB10_A2:

in rasterizer_gles3.cpp :: _blit_render_target_to_screen

+++ b/drivers/gles3/rasterizer_gles3.cpp
@@ -305,7 +305,9 @@ void RasterizerGLES3::_blit_render_target_to_screen(RID p_render_target, Display
                glBindFramebuffer(GL_READ_FRAMEBUFFER, read_fbo);
                glFramebufferTextureLayer(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, rt->color, 0, p_layer);
        } else {
-               glBindFramebuffer(GL_READ_FRAMEBUFFER, rt->fbo);
+    glGenFramebuffers(1, &read_fbo);
+    glBindFramebuffer(GL_READ_FRAMEBUFFER, read_fbo);
+    glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, rt->color,  0);
        }

this basically creates a temporary fbo with only the color attachment right before blitting to the screen (similar to what happens in XR with view_count > 1)

I have no idea why this works and the regular fbo does not, the only difference between them is that rt->fbo has a depth buffer attached as well.

Any ideas?

[akien-mga]

Fixed by #74945.