CST 325 - Graphics Programming (Week 6)

Light Transport

Concepts

-          Surface Interaction: transmission – pass through; specular – reflect through mirrored direction; diffuse – reflect uniformly; absorption – absorbed into the material; emission – a source of light

-          BRDF: Bidirectional Reflectance Distribution Function, which is the percentage of light reflects toward the eye. The function returns the probability of much light comes in and goes out. It is called Bidirectional because it is Symmetric. Switching the in and out gives the same result.

-          Rendering Equation: account for light that reaches x from any valid direction. It is recursive and has no analytic solution. We need to calculate how light moves from other surfaces throughout the entire scene.

-          Global vs Local Illumination: direct and indirect are both lights bouncing from surface to eye. Direct only bounce at most one and indirect bounce multiple times. Local Illumination only has Direct light, which is easy for rasterization (Indirect is fake with constant minimum value). Global Illumination has both. It’s costly and Path Tracing is the best approximation.

-          Lightmapping: a way to render light by precomputing and store in textures as second set of UV coordinates (grayscale values). However, the light and geometry cannot move, change direction and intensity. However, it laid a foundation for half – measure for dynamic global illumination.

-          Ambient & Phong Lighting: ambient light is constant to all surfaces of geometry. It approximates the effect of indirect lighting with minimum brightness of 10%. Phong lighting is a combination of ambient light + diffuse lighting + specular lighting, which gives a higher detail of depth and color for the same geometry.

-          Basic Light Source: Point light emanates light in all direction (light calculation - light source’s position and distance). Directional light comes from the same direction (light calculation - light source’s position). Spotlight comes from one point to a concentrated area, with inside (umbra) and outside (penumbra) angle. Inside area doesn’t reduce light brightness like outside, and light calculation based on position and distance.

-          Light direction & Normals: two most critical elements in light calculation. Illustration evolves based on light direction and normal per face, vertex or pixel. The evolution: flat shading, Gouraud shading, Phong shading, better Phong shading.

Application

This week’s programming assignment is the most challenge so far (beside the reflection that I didn’t try). However, the achievement after completing it is very satisfying, turning the frustration and challenges into fun and enjoyable experiences. So many times, I laughed at my own failed results or feeling amazed with the success ones (I love color transitioning effect).

Starting with the weekly material as usual, I was overwhelmed due to lots of combining information from last week. In addition, the appearance of the final project on the last video made me feel nervous. I have to account for many things, and I understood that I need to complete this week’s programming assignment thoroughly in order to work on the final project. So, want it or not, I had to start working on the programming assignment with unclear and overwhelming knowledge in my mind.

But the first few Todos were not as bad as I expected. There were a few obstacles, but I managed to get through while asking ChatGPT to clarify some materials along the way (especially with Phong Shading). The major problems began when I started working with a light position. Time after time, I had to find a way to work from Matrix to Vector, and Vector to Matrix (hard to keep track many times). Meanwhile, passing to the shaders wasn’t easy either. However, I tried different approaches, debugged the coordinates onto console, and developed my theory and plan before asking the ChatGPT to clarify. However, there were many times ChatGPT tried to guide me in different ways with its code, so I had to develop my own way, such as Matrix.multiplying(Vector). ChatGPT didn’t know that and gave me: Vector.multiplying(Matrix).

And lastly, the most important part of this assignment that is necessary for the final: rotating the light sphere. I remembered previously in Programming Assignment Week 3 where I had to rotate the moon similarly. However, at that time I was making the rotation matrix only. Then, I remember the earth – moon rotation where I had to combine many matrices. That gave me a hint in order to make the light, and the light sphere rotate as I need.

Now, feeling more confident, I believe I can handle the final project (or at least the rotation of all planets). Besides feeling nervous, excitement is also feeling up inside my mind. Of course, there are other elements such as shading, lighting, geometry that I need to worry about, but this programming assignment made me ‘believe’.

Visual Documentation