From 78207eac9b9b576ae66731ea257103f84b0ea41b Mon Sep 17 00:00:00 2001
From: Jacques Lucke <mail@jlucke.com>
Date: Wed, 14 Nov 2018 18:41:28 +0100
Subject: Py API Docs: New custom shader example

---
 doc/python_api/examples/gpu.11.py | 61 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 doc/python_api/examples/gpu.11.py

(limited to 'doc/python_api/examples')

diff --git a/doc/python_api/examples/gpu.11.py b/doc/python_api/examples/gpu.11.py
new file mode 100644
index 00000000000..61e7a842a59
--- /dev/null
+++ b/doc/python_api/examples/gpu.11.py
@@ -0,0 +1,61 @@
+"""
+Custom Shader for dotted 3D Line
+--------------------------------
+
+In this example the arc length (distance to the first point on the line) is calculated in every vertex.
+Between the vertex and fragment shader that value is automatically interpolated for all points that will be visible on the screen.
+In the fragment shader the `sin` of the arc length is calculated.
+Based on the result a decision is made on whether the fragment should be drawn or not.
+"""
+import bpy
+import gpu
+from random import random
+from mathutils import Vector
+from gpu_extras.batch import batch_for_shader
+
+vertex_shader = '''
+    uniform mat4 u_ViewProjectionMatrix;
+
+    in vec3 position;
+    in float arcLength;
+
+    out float v_ArcLength;
+
+    void main()
+    {
+        v_ArcLength = arcLength;
+        gl_Position = u_ViewProjectionMatrix * vec4(position, 1.0f);
+    }
+'''
+
+fragment_shader = '''
+    uniform float u_Scale;
+
+    in float v_ArcLength;
+
+    void main()
+    {
+        if (step(sin(v_ArcLength * u_Scale), 0.5) == 1) discard;
+        gl_FragColor = vec4(1.0);
+    }
+'''
+
+coords = [Vector((random(), random(), random())) * 5 for _ in range(5)]
+
+arc_lengths = [0]
+for a, b in zip(coords[:-1], coords[1:]):
+    arc_lengths.append(arc_lengths[-1] + (a - b).length)
+
+shader = gpu.types.GPUShader(vertex_shader, fragment_shader)
+batch = batch_for_shader(shader, 'LINE_STRIP',
+    {"position" : coords,
+     "arcLength" : arc_lengths})
+
+def draw():
+    shader.bind()
+    matrix = bpy.context.region_data.perspective_matrix
+    shader.uniform_float("u_ViewProjectionMatrix", matrix)
+    shader.uniform_float("u_Scale", 10)
+    batch.draw(shader)
+
+bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_VIEW')
\ No newline at end of file
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