texelFetchOffset wrong value on Android?

[MortimerGoro]

Hello,

I'm researching some Android problems (#17621 and #17851). I found that both problems happen on some Android devices (Google Pixel and Nexus 6) but work ok in Samsung Galaxy 7.

I have created a small test with just a 262x372 image in a html and the image is upside down on Google Pixel but ok in S7.

Doing some tests in the ps_image.vs shader I found that the image.sub_rect contains [-1.0, -1.0, -1.0, -1.0] values as expected on the S7, but [262.0, 372.0, 0.0, 0.0] values in the Google Pixel, causing it to go to the else branch.

if (image.sub_rect.x < 0.0) {
    uv0 = res.uv_rect.xy;
    uv1 = res.uv_rect.zw;
} else {
    uv0 = res.uv_rect.xy + image.sub_rect.xy;
    uv1 = res.uv_rect.xy + image.sub_rect.zw;
}

Another hint on the Google Pixel: image.sub_rect == image.stretch_size_and_tile_spacing. This values are got using the resource cache:

Image fetch_image(int address) {
    vec4 data[2] = fetch_from_resource_cache_2(address);
    return Image(data[0], data[1]);
}

It seems that the texelFetchOffset function is getting the same values for both vec4s on the Pixel. It doesn't make any sense because I printed the sResourceCache texture contents after each update from PBO (creating a helper FBO and using readPixels) and it contains the expected values in the primitive address sent in instanced :

draw_instanced_batch: [PrimitiveInstance { data: [1016, 0, 2147483647, 0, 0, 2050, 0, 0] }]

Pixel 1016x0: 8 8 262 372
Pixel 1017x0: 8 8 262 372
Pixel 1018x0: 262 372 0 0 // pi.prim_address + VECS_PER_PRIM_HEADER = 1016 + 2 = 1018
Pixel 1019x0: -1 -1 -1 -1

The sResourceCache texture contents of Pixel and S7 are exactly the same, but the texelFetchOffset call from fetch_image(prim.specific_prim_address) is getting different values on each device. Any idea what might be going on? I tried to change texture filters and increase sCacheTextureSize to test if the problem only happens in the texture border uvs but no luck yet.

[MortimerGoro]

ups, I wanted to create this on Webrender repo, not in Servo. Moved to servo/webrender#1694