Practical assignment #2

Assignment presentation

• Prepare a 2 min video presenting your software;
• Share the link to your GIThub repo through this form;
• The practical assignment has to reside in a branch named PA2.

Requirements

    Use sources from PA#1 adding a new functionality as follows:

• Render the surface with filled triangles using VBO (Vertex Buffer Object) technology with indices;
• Add two sliders providing ability to control surface granularity over U and V directions;
• Implement triangle shading method as per variant;
• Implement vertex and pixel shaders that calculate intensity of illumination for the surface coming from a single light source: I_rgb=Ambient+Diffuse+Specular that rotates in a circular motion around the surface. 

Resources

    The project we started to code at the lecture is here WebGL branch PA2

Details on Vertex Normals Calculation

    Pass the vertex normals as vertex attributes to GPU.

• Analytic normal: implement the function calculating normal as a cross product of  partial derivatives (tangent vectors) along U and V directions of your surface, normalize the result;
• Facet Average normal: sum all facet normals that are adjacent to the vertex to form a vertex normal, normalize the result;
• Facet Area Weighted Average normal: sum all facet normals that are adjacent to the vertex to form a vertex normal using area as a weight coefficient, normalize the result;
• Facet Angle Weighted Average normal: sum all facet normals that are adjacent to the vertex to form a vertex normal using angle as a weight coefficient, normalize the result.

Details on Gouraud/Phong shading

    Implement the necessary code in .js and/or vertex/fragment shader.

Details on a point light source

• pass coordinates of a light source to GPU as uniform parameter;
• do not forget to multiply the coordinates by ModelView matrix before passing them to GPU.

Details on projection

    use single point perspective/orthographic matrix.

Hint

• when calculating specular component you can take (0,0,1) direction vector as the vector pointing towards the viewer instead of calculating per-pixel direction (global viewer model);
• intensity of the light source components can be hardcoded in the shader;
• you can calculate the world coordinates of each point in fragment shader  interpolating vertex coordinates using hardware interpolator (varying keyword);
• If you need to interpolate normals along primitive pass them to fragment shader using varying keyword.

Variant*		Shading Gouraud	Shading Phong		Vertex Normal Analytic	Vertex Normal Facet average	Vertex Normal Facet Area Weighted average	Vertex Normal Facet Angle Weighted average
1			V		V
2		V				V
3			V				V
4		V						V
5			V					V
6		V					V
7			V			V
8		V			V
9			V		V
10		V				V
11			V				V
12		V						V
13			V					V
14		V					V
15			V			V
16		V			V
17			V		V
18		V				V
19			V				V
20		V						V
21			V					V
22		V					V
23			V			V
24		V			V
25			V		V
26		V				V
27			V				V
28		V						V
29			V
30		V

*Variants higher than 30 start over from 1