The emulator was blamed for two days for what is iris's own defect on any
GL adapter. `GpuTextures::new` created the atlas `texture_2d_array` with
one layer; wgpu-hal picks the GL target from the descriptor alone
(`gles::Texture::get_info_from_desc`, `(false, 1) => TEXTURE_2D`), so the
shader's `sampler2DArray` was handed a `GL_TEXTURE_2D`, the unit was
incomplete, every `textureSample` returned (0,0,0,1), and `draw_glyph`'s
`color.a *= texel.a` painted the whole glyph quad.
`MIN_ARRAY_LAYERS = 2`, with the account at `create_array_texture` and a
`debug_assert!` there. Vulkan -- the phone's build and the desktop's
default backend -- was never affected.
`force-gles` now switches the desktop backend too, so the GLES path is
reproducible on a machine with a real GPU in seconds rather than only
through an APK: that is how this was found, with two shader probes
showing the sample was exactly (0,0,0,1).
iris
3cb18ac5c2