new documentation for GPU backend.

hartsantler · hartsantler · commit fe1e2a9effac · 2014-06-18T01:37:24.000-07:00
diff --git a/doc/gpu.md b/doc/gpu.md
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+GPU Translation
+---------------
+A subset of Python with extra type information can be translated into a GLSL fragment shader.  The `@gpu` decorator marks a function for translation to GLSL.  All variables inside the function must be typed using GLSL types.  You can type your variables using decorators or special PythonJS type syntax.
+
+Typing with Decorators
+----------------------
+
+```
+	@returns( array=[512,512] )
+	@typedef( x=float, y=float, tempX=float, i=int, runaway=int, c=vec2)
+	@gpu.main
+	def gpu_mandelbrot():
+		c = get_global_id()
+		x = 0.0
+		y = 0.0
+		tempX = 0.0
+		i = 0
+		runaway = 0
+		for i in range(100):
+			tempX = x * x - y * y + float(c.x)
+			y = 2.0 * x * y + float(c.y)
+			x = tempX
+			if runaway == 0 and x * x + y * y > 100.0:
+				runaway = i
+		return float(runaway) * 0.01
+
+```
+
+
+Typing C-style
+----------------------
+
+```
+	@returns( array=[512,512] )
+	@gpu.main
+	def gpu_mandelbrot():
+		vec2 c = get_global_id()
+		float x = 0.0
+		float y = 0.0
+		float tempX = 0.0
+		int i = 0
+		int runaway = 0
+		for i in range(100):
+			tempX = x * x - y * y + float(c.x)
+			y = 2.0 * x * y + float(c.y)
+			x = tempX
+			if runaway == 0 and x * x + y * y > 100.0:
+				runaway = i
+		return float(runaway) * 0.01
+
+```
+
+@returns
+---------
+The main entry point function marked with `@gpu.main` must also use the `@returns(array=[w,h])` decorator to declare the width and height of the 2D array that it will return. Subroutines must also use the `@returns` decorator to declare their GLSL return type like this: `@returns(float)`
+
+
+get_global_id()
+--------------
+The GLSL function `get_global_id()` is part of the WebCLGL API and returns a vec2 that contains the current `x` and `y` index.
