ARB fragment INSTRUCTIONS

  • CMP dest, src0, src1, src2
    Choose src1 if src0 >= 0. Otherwise, choose src2. The comparison is done per channel.
dest = ((src0 >= 0) ? 1.0 : 0.0) * (src1 - src2) + src2

  • LRP dest, src0, src1, src2
    Interpolates linearly between the second and third source registers by a proportion specified in the first source register.
dest = src0 * src1 + (1-src0) * src2
// which is the same as
dest = src2 + src0 * (src1 - src2)

The above explain is different from ARB fragment, is equal to

ADD result src0, -src2
MAD result, result, src1, src2
dest = (src0 - src2) * src1 + src2  // proportion specified in src1
  • .xyzw 后缀与默认后缀
r0.zw = tex2D(_MainTex, i.tex0); 
// tex2D的返回内容为float4, 把它内容传递给 r0.zw 时，默认下会取 .xy 也即：r0.zw = tex2D(_MainTex, i.tex0).xy;
// 若该指令是从一条汇编指令直译过来，其正确写法为：r0.zw = tex2D(_MainTex, i.tex0).zw;

r0.z = max(r0, r1.w);
// max()函数中的 r0 默认后缀为 .x，上面等价于 r0.z = max(r0.x, r1.w);
// 实际上该式子应该为: r0.z = max(r0.z, r1.w);

// 结论：根据目标寄存器所采用的xyzw分量的数目，会自动选择源寄存器中对应的分量组合：.x  .xy  .xyz  .xyzw 
// 若要有意选择 .y .z .w  .yz .zw 等分量，则需要明确填写
posted @ 2024-11-04 12:06  opencoder  阅读(5)  评论(0)  编辑  收藏  举报