Galactica/crates/render/shaders/include/anchor.wgsl

// Given an anchored position and sprite dimensions,
// return the translation that should be applied on
// vertex coordinates
fn anchor(
	anchor: u32,         // Anchor index
	position: vec2<f32>, // Anchored position
	dim: vec2<f32>,      // Sprite dimensions (width, height)
) -> vec2<f32> {

	// TODO: remove, do in ui rust lib
	var trans: vec2<f32> = vec2(0.0, 0.0);
	let window_dim = (
		vec2(global_data.window_size_w, global_data.window_size_h) /
		global_data.window_scale
	);

	if anchor == 0u { // NW C (screen anchor, sprite anchor)
		trans += vec2(-window_dim.x, window_dim.y) / 2.0; // origin
		trans += vec2(0.0, 0.0) / 2.0; // offset
	} else if anchor == 1u { // NW NW
		trans += vec2(-window_dim.x, window_dim.y) / 2.0;
		trans += vec2(dim.x, -dim.y) / 2.0;
	} else if anchor == 2u { // NW NE
		trans += vec2(-window_dim.x, window_dim.y) / 2.0;
		trans += vec2(-dim.x, -dim.y) / 2.0;
	} else if anchor == 3u { // NW SW
		trans += vec2(-window_dim.x, window_dim.y) / 2.0;
		trans += vec2(dim.x, dim.y) / 2.0;
	} else if anchor == 4u { // NW SE
		trans += vec2(-window_dim.x, window_dim.y) / 2.0;
		trans += vec2(-dim.x, dim.y) / 2.0;
	} else if anchor == 5u { // NE NE
		trans += vec2(window_dim.x, window_dim.y) / 2.0;
		trans += vec2(-dim.x, -dim.y) / 2.0;
	} else if anchor == 6u { // C C
		trans += vec2(0.0, 0.0) / 2.0;
		trans += vec2(0.0, 0.0) / 2.0;
	} else if anchor == 7u { // C NW
		trans += vec2(0.0, 0.0) / 2.0;
		trans += vec2(dim.x, -dim.y) / 2.0;
	} else { // center / center as default, since it's the most visible variant.
		trans += vec2(0.0, 0.0) / 2.0;
		trans += vec2(0.0, 0.0) / 2.0;
	}

	trans += position;

	// This renders correctly, but the offsets here are off by a factor of two.
	// I'm not sure why... might be because WGPU screen coordinates are -1 to 1.
	return (trans / window_dim) * 2.0;
}