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--- guides:gpu [2024/05/31 22:38] – osnr
+++ guides:gpu [2024/07/16 20:20] (current) – Add time, remove TODO b/c it works admin
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+====== GPU FFI ======
 The new 'GPU FFI' lets you write vertex and fragment shaders to draw things.
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 You can make ''%%sampler2D%%''-type arguments if you want to pass an image in; you can make ''%%fn%%'' arguments to a fragment shader as third argument. See the implementations of drawing primitives in virtual-programs/display/*.folk for more examples.
+====== Adding functions ======
+When you want to use functions, maybe to [[https://iquilezles.org/articles/palettes/|start using fun new color palettes in your shaders]], you can add them like this:
+<code>
+# source: https://iquilezles.org/articles/palettes/
+# cosine based palette, 4 vec3 params
+Wish the GPU compiles function "palette" {{float t vec3 a vec3 b vec3 c vec3 d} vec3 {
+    return a + b*cos( 6.28318*(c*t+d) );
+}}
+Wish the GPU compiles pipeline "$this's triangle" {
+    {vec2 p0 vec2 p1 vec2 p2 float u_time} {
+        vec2 vertices[4] = vec2[4](p0, p1, p2, p0);
+        return vertices[gl_VertexIndex];
+    } {fn palette} {
+        vec3 gradientColor = palette(gl_FragCoord.x, vec3(0.5,0.5,0.5),vec3(sin(u_time),0.5,0.5),vec3(1.0,1.0,1.0),vec3(0.0,sin(u_time),0.20));
+        return vec4(gradientColor, 1.0);
+    }
+}
+Wish $this is outlined blue
+When $this has region /r/ & the clock time is /t/ {
+    set r' [region move $r down 100%]
+    Wish the GPU draws pipeline "$this's triangle" with arguments [list {*}[lrange [region vertices ${r'}] 0 2] [fmod $t 16384]]
+}</code>
 ==== TODO: Document internal Gpu:: API ====