From 406452ec5d9ab3054800a31b32cfc5275592bd61 Mon Sep 17 00:00:00 2001
From: Jacques Lucke <mail@jlucke.com>
Date: Mon, 12 Nov 2018 17:17:59 +0100
Subject: Py API Docs: Another example for offscreen rendering

---
 doc/python_api/examples/gpu.8.py | 83 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 doc/python_api/examples/gpu.8.py

diff --git a/doc/python_api/examples/gpu.8.py b/doc/python_api/examples/gpu.8.py
new file mode 100644
index 00000000000..187276d61f5
--- /dev/null
+++ b/doc/python_api/examples/gpu.8.py
@@ -0,0 +1,83 @@
+"""
+Generate a texture using Offscreen Rendering
+--------------------------------------------
+
+1. Create an :class:`gpu.types.GPUOffScreen` object.
+2. Draw some circles into it.
+3. Make a new shader for drawing a planar texture in 3D.
+4. Draw the generated texture using the new shader.
+"""
+import bpy
+import gpu
+import bgl
+from mathutils import Matrix
+from gpu_extras.batch import batch_for_shader
+from gpu_extras.presets import draw_circle_2d
+
+# Create and fill offscreen
+##########################################
+
+offscreen = gpu.types.GPUOffScreen(512, 512)
+
+offscreen.bind()
+try:
+    bgl.glClear(bgl.GL_COLOR_BUFFER_BIT)
+    with gpu.matrix.push_pop():
+        gpu.matrix.load_matrix(Matrix.Identity(4))
+        gpu.matrix.load_projection_matrix(Matrix.Identity(4))
+
+        amount = 10
+        for i in range(-amount, amount + 1):
+            x_pos = i / amount
+            draw_circle_2d((x_pos, 0.0), (1, 1, 1, 1), 0.5, 200)
+finally:
+    offscreen.unbind()
+
+
+# Drawing the generated texture in 3D space
+#############################################
+
+vertex_shader = '''
+    uniform mat4 modelMatrix;
+    uniform mat4 viewProjectionMatrix;
+
+    in vec2 position;
+    in vec2 uv;
+
+    out vec2 uvInterp;
+
+    void main()
+    {
+        uvInterp = uv;
+        gl_Position = viewProjectionMatrix * modelMatrix * vec4(position, 0.0, 1.0);
+    }
+'''
+
+fragment_shader = '''
+    uniform sampler2D image;
+
+    in vec2 uvInterp;
+
+    void main()
+    {
+        gl_FragColor = texture(image, uvInterp);
+    }
+'''
+
+shader = gpu.types.GPUShader(vertex_shader, fragment_shader)
+batch = batch_for_shader(shader, 'TRI_FAN',
+    {"position" : ((-1, -1), (1, -1), (1, 1), (-1, 1)),
+     "uv" : ((0, 0), (1, 0), (1, 1), (0, 1))})
+
+
+def draw():
+    bgl.glActiveTexture(bgl.GL_TEXTURE0)
+    bgl.glBindTexture(bgl.GL_TEXTURE_2D, offscreen.color_texture)
+
+    shader.bind()
+    shader.uniform_float("modelMatrix", Matrix.Translation((1, 2, 3)) @ Matrix.Scale(3, 4))
+    shader.uniform_float("viewProjectionMatrix", bpy.context.region_data.perspective_matrix)
+    shader.uniform_float("image", 0)
+    batch.draw(shader)
+
+bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_VIEW')
\ No newline at end of file
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