OpenGL programming easy to get started special effect operation (1)

Each object has a different visual effect in different environments. Special effects need to be added to make the effect more real.

Example 8: Draws three overlapping rectangles, which are green, red, and blue from left to right respectively. The transparency of the red and blue rectangles is 50% transparency, that is, the alpha value is 0.5, as shown in figure nine.

#include <stdlib.h> #include <GL/glut.h> void Myinit (void) { Glclearcolor (0.2,0.8,0.8,0.0)//Set Background to Lake Blue Glenable (gl_blend);//Activate Gl_blend Glblendfunc (Gl_src_alpha,gl_one_minus_src_alpha);//The mathematical algorithm for specifying pixels Glenable (Gl_flat); } void Mydisplay (void) { Glclear (Gl_color_buffer_bit); /* Draw a green rectangle alpha = 1.0*/ glcolor4f (0.0,1.0,0.0,1.0); Glbegin (Gl_polygon); glvertex3f ( -0.75,0.5,0.0); glvertex3f ( -0.75,-0.75,0.0); glvertex3f (0.5,-0.75,0.0); glvertex3f (0.5,0.5,0.0); Glend (); /* Draw a red rectangle alpha = 0.5*/ glcolor4f (1.0,0.0,0.0,0.5); Glbegin (Gl_polygon); glvertex3f ( -0.25,1.0,0.0); glvertex3f ( -0.25,-0.25,0.0); glvertex3f (1.0,-0.25,0.0); glvertex3f (1.0,1.0,0.0); Glend (); /* Draw a blue rectangle alpha = 0.5*/ glcolor4f (0.0,0.0,1.0,0.5); Glbegin (Gl_polygon); glvertex3f (0.25,1.5,0.0); glvertex3f (0.25,0.25,0.0); glvertex3f (1.5,0.25,0.0); glvertex3f (1.5,1.5,0.0); Glend (); Glflush (); } void Myreshape (int w,int h) { Glviewport (0,0,W,H); Glmatrixmode (gl_projection); Glloadidentity (); if (wGlortho ( -1.5,1.5,-1.5* (glfloat) h/(glfloat) w,1.5* glfloat (h/) glfloat); Else Glortho ( -1.5* (glfloat) w/(glfloat) h,1.5* glfloat (w/) glfloat); Glmatrixmode (Gl_modelview); Glloadidentity (); Gltranslatef ( -0.4,0.0,0.0); } int main (int argc,char * * argv) { /* Initialize * * Glutinit (&AMP;ARGC,ARGV); Glutinitdisplaymode (glut_single| GLUT_RGB); Glutinitwindowsize (300,400); Glutinitwindowposition (200,200); /* Create window * * Glutcreatewindow ("BLEND POLYGON"); /* Draw and display * * Myinit (); Glutreshapefunc (Myreshape); Glutdisplayfunc (Mydisplay); /* Enter GLUT event handling cycle * * Glutmainloop (); return (0); }

Figure 9:3 A rectangle that overlaps each other

Glblendfunc (glenum sfactor,glenum dfactor) specifies the pixel algorithm. Sfactor specifies how the red, green, blue, and alpha source blending factors are calculated. Dfactor specifies how the red, green, blue, and alpha target blend factors are calculated.