Render more than ~5300 images

[taj-p]

Fixes #1468

There is a bug in the shader code - we only check the first row of the encoded paints texture. On my machine, that gives me ~5400 images before I start drawing empty rectangles.

This PR modifies our textureLoad calls to consider more than the first row of texels.

On my machine, I used the following test to verify the fix.

#[vello_test(width = 10, height = 10)]
fn image_many_unique_paints_wrap_encoded_texture(ctx: &mut impl Renderer) {
    const NUM_IMAGES: usize = 6000;
    let sampler = ImageSampler {
        x_extend: Extend::Pad,
        y_extend: Extend::Pad,
        quality: ImageQuality::Low,
        alpha: 1.0,
    };

    let dummy_rect = Rect::new(0.0, 0.0, 1.0, 1.0);
    for i in 0..NUM_IMAGES {
        let mut pix = Pixmap::new(1, 1);
        let val = (i % 255 + 1) as u8;
        pix.set_pixel(0, 0, PremulRgba8::from_u32(u32::from_be_bytes([val, val, val, 255])));
        let source = ctx.get_image_source(Arc::new(pix));
        ctx.set_paint(Image {
            image: source,
            sampler,
        });
        ctx.fill_rect(&dummy_rect);
    }

    let mut final_pix = Pixmap::new(1, 1);
    final_pix.set_pixel(0, 0, PremulRgba8::from_u32(u32::from_be_bytes([255, 0, 0, 255])));
    let final_source = ctx.get_image_source(Arc::new(final_pix));
    ctx.set_paint(Image {
        image: final_source,
        sampler,
    });
    ctx.fill_rect(&Rect::new(0.0, 0.0, 10.0, 10.0));
}

[grebmeg]

LGTM

[grebmeg]

Missing new line

[grebmeg]

I’d be interested in exploring passing the texture dimensions as a uniform later. I’m curious how it performs across different machines.

[taj-p]

Ohhh great idea. This would mimic what we do for alphas_tex_width_bits. Implemented in 050add1

[grebmeg]

If we can rely on max_texture_dimension_2d always being a power of two, we can use bitwise operations. We use the same pattern for alphas_texture.

[taj-p]

Great idea! Thank you! Implemented in 050add1

[LaurenzV]

I think if we set this to align(16), bytemuck will automatically complain in case there is not enough padding, which could be useful in case we change it again in the future

[taj-p]

Addressed in #1474

[LaurenzV]

Can we not use an array<3> here?

[taj-p]

That's not possible. Apparently for downleveling uniforms to WebGL2, arrays require a stride of 16 bytes. See the table in this section .

array<S> requires alignment roundUp(16, AlignOf(S)).

edit: How wild that it requires so much memory. A big pain point for uniforms!