Tutorial: Lighting Calculations

Exercises

In this tutorial:

1. Use a diffuse shader to apply lighting to geometry
2. Add Blinn-Phong specular highlights to the shader
3. Implement Blinn-Phong lighting per-pixel
4. Convert both Blinn-Phong shaders to calculate Phong lighting

1: The diffuse shader

• Use the base code from last tutorial to load and use this shader. diffuse.vert just applies diffuse and ambient lighting.
• Draw either a glutSolidSphere or some procedurally generated geometry with normals. Something that has adjustable tessellation.
• Experiment with the tessellation of your geometry and compare the visual result of the diffuse shader to OpenGL's fixed function lighting.

2: Add the specular highlights to the lighting shader

• Follow the Lighthouse 3D tutorial on GLSL to implement Blinn-Phong lighting.
• The Blinn-Phong lighting calculations use the "half vector" between the light and viewer direction vectors to approximately model the normal where the center of the specular highlight occurs.
• Since the viewer is at (0, 0, 0) in world space this viewer vector (or vector to the "camera") is negative gl_Vertex in eye-space.
• Again compare the results to fixed function lighting.

3: Per-Pixel shading

• Now create a copy of that per-vertex shader for our per-pixel lighting (still using Blinn-Phong calculations).

  

• Per-pixel lighting requires the lighting vectors (normal, light, viewer) to be interpolated instead of the colour from each vertex. Then the colour for each pixel is generated in the fragment shader using these interpolated vector values. Don't forget to normalize the vectors again after the interpolation.
• Follow the Lighthouse 3D tutorial for per-pixel lighting.
• What difference is there between per-vertex and per-pixel lighting: For a low number of polygons and high number, enough so the polygon size approaches the size of one pixel.

4: Phong lighting

• Instead of using the half vector for the specular highlight, Phong lighting calculations use the correct reflected vector of the light vector around the normal. GLSL has a reflect() function that can be used for this.

  

• Implement Phong lighting using per-vertex and then per-pixel shading.
• Look closely at the shape and spread of the specular highlight. What differences are there?
  Note that differences are expected. Manually scaling shininess in an attempt to match methods is incorrect.

Resources

• GLSL quick reference (old, small version)
• GLSL quick reference (khronos)