Reuse the texture2D result for color and alpha (#357)

.changeset/rude-clocks-trade.md

@@ -0,0 +1,5 @@
+---
+"shader-composer": patch
+---
+
+**Fixed:** `Texture2D().color` and `Texture2D().alpha` now reuse the sample `texture2D` call, instead of re-sampling the texture.

packages/shader-composer/src/stdlib/textures.ts

@@ -2,14 +2,18 @@ import { $ } from "../expressions"
 import { Input, Unit } from "../units"
 import { Float, Vec3, Vec4 } from "./values"
 
-export const Texture2D = (sampler2D: Unit<"sampler2D">, xy: Input<"vec2">) => ({
-	...Vec4($`texture2D(${sampler2D}, ${xy})`, {
-		name: "Texture2D"
-	}),
+export const Texture2D = (sampler2D: Unit<"sampler2D">, xy: Input<"vec2">) => {
+  const texture2D = Vec4($`texture2D(${sampler2D}, ${xy})`, {
+    name: "Texture2D"
+  })
 
-	/** The color value sampled from the texture. */
-	color: Vec3($`texture2D(${sampler2D}, ${xy}).rgb`, { name: "Texture2D Color" }),
+  return {
+    ...texture2D,
 
-	/** The alpha value sampled from the texture. */
-	alpha: Float($`texture2D(${sampler2D}, ${xy}).a`, { name: "Texture2D Alpha" })
-})
+    /** The color value sampled from the texture. */
+    color: Vec3($`${texture2D}.rgb`, { name: "Texture2D Color" }),
+
+    /** The alpha value sampled from the texture. */
+    alpha: Float($`${texture2D}.a`, { name: "Texture2D Alpha" })
+  }
+}