i want to shade the quad with checkers:
f(P)=[floor(Px)+floor(Py)]mod2.
My quad is:
glBegin(GL_QUADS);
glVerte
It is better to calculate this effect in fragment shader, something like that:
vertex program =>
varying vec2 texCoord;
void main(void)
{
gl_Position = vec4( gl_Vertex.xy, 0.0, 1.0 );
gl_Position = sign( gl_Position );
texCoord = (vec2( gl_Position.x, gl_Position.y )
+ vec2( 1.0 ) ) / vec2( 2.0 );
}
fragment program =>
#extension GL_EXT_gpu_shader4 : enable
uniform sampler2D Texture0;
varying vec2 texCoord;
void main(void)
{
ivec2 size = textureSize2D(Texture0,0);
float total = floor(texCoord.x*float(size.x)) +
floor(texCoord.y*float(size.y));
bool isEven = mod(total,2.0)==0.0;
vec4 col1 = vec4(0.0,0.0,0.0,1.0);
vec4 col2 = vec4(1.0,1.0,1.0,1.0);
gl_FragColor = (isEven)? col1:col2;
}
Output =>
Good luck!