LightingandSolidModeling.ppt

Lighting Models CIS 488/588 Bruce R. Maxim UM-Dearborn Lighting Huge topic in computer graphics Nearly all 3D rendering packages make use of ray tracing to determine the shadows and reflective surfaces in the screen images Software-based graphics engines cannot support the same complex lighting models that hardware (e.g. pixel and vertex shaders) Color Models Color can be represented using separate RGB values or using an index into a table Some RGB models use integers 0-255 for each color and some use real numbers with values 0.0-1.0 for each Float values are easier to work with mathematically, but integers can be faster for rendering since they can be written straight to the video buffer Color Addition When adding two RGB integer colors you need to catch overflow problems C1 = (r1, g1, b1) C2 = (r2, g2, b2) C = C1 + C2 C = (max(r1 + r2, 255), max(r1 + r2, 255), max(r1 + r2, 255)) Color Modulation Color modulation is basically multiplication Can be done using a real scalar (brightness modulation) or by multiplying the RGB values in a pairwise manner C1 = (r1, g1, b1) C2 = (r2, g2, b2) C = s * C1 = (s * r1, s *g1, s * b1) C = C1 * C2 = (r1 * r2, g1 * g2, b1 * b2) Again, we need to beware of overflow Demo8_1 // copy texture into temp for rendering and scaling Copy_Bitmap(temp_text,0,0, textures[curr_texture],0,0,TEXTSIZE, TEXTSIZE); ? /////////////////////////////////////////// // our little image processing algorithm :) //Cmodulated = s*C1 = (s*r1, s*g1, s*b1) ? USHORT *pbuffer = (USHORT *)temp_text.buffer; ? Demo8_1 // perform RGB transformation on bitmap for (int iy = 0; iy temp_text.height; iy++) for (int ix = 0; ix temp_text.width; ix++) { USHORT pixel = pbuffer[iy*temp_text.width + ix]; int ri,gi,bi; // used to extract the rgb values _RGB565FROM16BIT(pixel, ri,gi,bi); // perform scaling operation and test for overflow if ((ri = (float)ri * scalef) 255) ri=255; if ((gi = (float)gi * scalef) 255) gi=25