Tips/tricks related to Computer Graphics, GPUs and other programming

Posts tagged ‘beginner’

Getting started with OpenGL ES 2.0 shaders on Android

Tutorials on how to write shaders for the Android platform are a little difficult to come by on the Internet, so I decided to work on a small but simple program which hopefully provides a simple framework to get started writing programs for OpenGL ES 2.0.

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I’ll first link to the apk, source code and the repository:
apk here.
Source code here.
Google Code Repository  here. NOTE: Branch is “default”
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Here’s what my program does:

  • Mesh Loading:The program loads triangular meshes in these formats (as .txt files):
    • (.OFF): These consist of only vertex positions. My program will calculate per-vertex normals.
    • (.OBJ): Vertex positions, normals and texture coordinates are provided. Sample textured cube mesh was exported from Blender.
  • Shaders:
    • Gouraud Shading: Per-vertex lighting [with texture mapping if enabled].
    • Phong Shading: Per-pixel lighting [with texture mapping if enabled].
    • Normal Mapping: Gives a fake appearance of depth to a mesh. Sample normal map included.

NOTE: If your program is crashing with glError 1281 and you have a relatively new phone (a Samsung Galaxy S2 for example), change all dot() method calls in the shaders to dot2().

How it works:

The program will only work if your phone supports OpenGL ES 2.0. If it doesn’t my program quits without a warning.

When the program starts you will see an octahedron mesh with Gouraud shading enabled. There is a light rotating around the mesh. You can use one finger
to rotate the mesh, and two fingers (pinch-to-zoom) to scale the mesh (though it’s not *perfect* ). Clicking the menu button on your phone allows you to:

  • Toggle Light Rotation: Light rotation can be toggled through this option. A short ‘Toast’ notification pops up.
  • Shader switching: Can switch between Gouraud shading, phong shading and normal mapping.
  • Mesh switching: Can switch between an Octahedron, Tetrahedron (both .off files) and Textured Cube Mesh (.obj file).
  • Toggle Texturing: Can turn off texture mapping if there is an associated texture with the object (only the textured cube mesh).


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