From e937ac372fa92cd971d344748978a08316a55db4 Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Sun, 16 Aug 2026 18:37:24 -0700
Subject: instance buffer, rotation

---
 src/shader/shader.wgsl | 69 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 48 insertions(+), 21 deletions(-)

(limited to 'src/shader')

diff --git a/src/shader/shader.wgsl b/src/shader/shader.wgsl
index 9baa4b7..fb1e0b1 100644
--- a/src/shader/shader.wgsl
+++ b/src/shader/shader.wgsl
@@ -1,44 +1,71 @@
-struct ChunkData {
-    origin: vec2<i32>,
-};
-
-var<immediate> chunk: ChunkData;
-
 struct Camera {
     scale: vec2f,
     centre: vec2f,
 };
 
+struct Instance {
+    centre: vec2f,
+    cos_sin: vec2f,
+    half_size: vec2f,
+    dims: vec2u,
+    cell_offset: u32,
+};
+
 @group(0) @binding(0) var<uniform> camera: Camera;
-@group(1) @binding(0) var tex: texture_2d<f32>;
+@group(0) @binding(1) var<storage, read> palette: array<vec4f>;
+@group(0) @binding(2) var<storage, read> instances: array<Instance>;
+@group(0) @binding(3) var<storage, read> cells: array<u32>;
 
 struct VertexOutput {
     @builtin(position) clip_position: vec4<f32>,
-    @location(0) uv: vec2<f32>,
+    @location(0) world: vec2<f32>,
+    @location(1) @interpolate(flat) instance: u32,
 };
 
 @vertex
 fn vs_main(
     @builtin(vertex_index) i: u32,
+    @builtin(instance_index) n: u32,
 ) -> VertexOutput {
-    var out: VertexOutput;
-    // (0,0),(1,0),(0,1),(1,1)
-    let corner = vec2f(f32(i & 1u), f32(i >> 1u));
+    let instance = instances[n];
 
-    // CHUNK_SIZE
-    let world = (vec2f(chunk.origin) + corner * 128);
-    let ndc = (world - camera.centre) * camera.scale;
+    // (-1,-1),(1,-1),(-1,1),(1,1)
+    let corner = vec2f(f32(i & 1u), f32(i >> 1u)) * 2.0 - 1.0;
+    let local = corner * (instance.half_size + 2.0);
+    let world = instance.centre + vec2f(
+        local.x * instance.cos_sin.x - local.y * instance.cos_sin.y,
+        local.x * instance.cos_sin.y + local.y * instance.cos_sin.x,
+    );
 
-    out.clip_position = vec4f(ndc, 0.0, 1.0);
-    out.uv = corner;
+    var out: VertexOutput;
+    out.clip_position = vec4f((world - camera.centre) * camera.scale, 0.0, 1.0);
+    out.world = world;
+    out.instance = n;
 
     return out;
 }
 
 @fragment
 fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
-    // CHUNK_SIZE
-    let dims = vec2f(128.0, 128.0);
-    return textureLoad(tex, vec2i(in.uv * dims), 0);
-    // return vec4f(0.0, 1.0, 0.0, 1.0);
-}
\ No newline at end of file
+    let instance = instances[in.instance];
+
+    let d = in.world - instance.centre;
+    let q = floor(d) + vec2f(0.5);
+    let local = vec2f(
+        q.x * instance.cos_sin.x + q.y * instance.cos_sin.y,
+        -q.x * instance.cos_sin.y + q.y * instance.cos_sin.x,
+    ) + instance.half_size;
+
+    let cell = vec2i(floor(local));
+    if any(cell < vec2i(0)) || any(cell >= vec2i(instance.dims)) {
+        discard;
+    }
+
+    let idx = instance.cell_offset + u32(cell.y) * instance.dims.x + u32(cell.x);
+    let material = (cells[idx >> 2u] >> ((idx & 3u) * 8u)) & 0xFFu;
+    if material == 0u {
+        discard;
+    }
+
+    return palette[material];
+}
-- 
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