refactor(wgsl): Factorize getScreenCoord helper

Factorizes the screen coordinate calculation from scene1.wgsl into a reusable getScreenCoord function in common/shaders/math/common_utils.wgsl.

This improves code reuse and simplifies fragment shaders.

1 files changed, 10 insertions, 0 deletions

diff --git a/common/shaders/math/common_utils.wgsl b/common/shaders/math/common_utils.wgsl
index 7131216..49aaead 100644
--- a/common/shaders/math/common_utils.wgsl
+++ b/common/shaders/math/common_utils.wgsl
@@ -34,3 +34,13 @@ fn grid_pattern(uv: vec2<f32>) -> f32 {
 
 // NOTE: calc_sdf_normal_bumped() removed - too specialized, depends on get_dist()
 // from scene_query snippets. Keep bump mapping code inline in shaders that use it.
+
+// Calculates normalized screen coordinates from fragment position and resolution.
+// Input `p` is the fragment's @builtin(position), `resolution` is the screen resolution.
+// Returns a vec2<f32> in NDC space, with X adjusted for aspect ratio.
+fn getScreenCoord(p: vec4<f32>, resolution: vec2<f32>) -> vec2<f32> {
+    let q = p.xy / resolution;
+    var coord = -1.0 + 2.0 * q;
+    coord.x *= resolution.x / resolution.y;
+    return coord;
+}