GLSL 棋盘格图案

Question

我想用跳棋来遮蔽四边形:

f(P)=[floor(Px)+floor(Py)]mod2.

我的四边形是:

glBegin(GL_QUADS);    
  glVertex3f(0,0,0.0);    
  glVertex3f(4,0,0.0);    
  glVertex3f(4,4,0.0);   
  glVertex3f(0,4, 0.0); 
glEnd();

顶点着色器文件:

varying float factor;
float x,y;
void main(){
  x=floor(gl_Position.x);
  y=floor(gl_Position.y);
  factor = mod((x+y),2.0);
}

片段着色器文件是:

varying float factor;
void main(){
  gl_FragColor = vec4(factor,factor,factor,1.0);
}

但我得到了这个:



似乎 mod 功能不起作用或者其他东西......
有什么帮助吗？

Answer 1

最好在片段着色器中计算这种效果，如下所示:

顶点程序 =>

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 );      
}

片段程序 =>

#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;
}

输出 =>



祝你好运!