在纹理的一半上应用投影

Question

我正在使用三个 glcontrols 说 GlControl1、GlControl2、GlControl3。 我有两个纹理 stexture1 和 stexture2。 stexture1 在 glcontrol2 中显示的位置。 stexture2 的右半部分显示在 glcontrol1 上，左半部分显示在 glcontrol3 上。 现在我想在这三个 glcontrols 上应用投影。使用这个link，我可以在glcontrol2 上成功应用它，因为它可以完全显示纹理。

但是在 glcontrol1 和 glcontrol3 上应用时，它不能正常工作。

请查看我正在尝试的着色器代码。

   GL.ShaderSource(fragShader, @"precision highp float;
    uniform sampler2D sTexture_1;
    uniform sampler2D sTexture_2;
    uniform float sSelectedRangeLeft;   
    uniform float sSelectedRangeRight;
    uniform float sSelectedRangeLeftEnd;   
    uniform float sSelectedRangeRightEnd;     
    uniform int sCurrentGLControl;
    varying vec2 vTexCoordIn;
    void main ()
    {
    vec2 vTexCoord=vec2(vTexCoordIn.x,vTexCoordIn.y);

   float rightsliderStartval=sSelectedRangeRight;//0.5(value between 0.5 and 1.0)
   float rightsliderEndval=sSelectedRangeRightEnd;//1.0(value between 0.5 and 1.0)
   float rightsliderDelta=rightsliderEndval-rightsliderStartval;

   float leftsliderStartval=sSelectedRangeLeftEnd;//0.0(value between 0 and 0.5)
   float leftsliderEndval=sSelectedRangeLeft;//0.5(value between 0 and 0.5)
   float leftsliderDelta=leftsliderEndval-leftsliderStartval;

 if(sCurrentGLControl==1)
 { 
 if ( vTexCoord.x <=1.0 &&  vTexCoord.x > 1.0 -rightsliderDelta)
 {
 vec4 colorLeft=texture2D (sTexture_2, vec2(vTexCoord.x -(1.0-rightsliderEndval), vTexCoord.y));
//i want to show this result in a projected view like glcontrol2
 gl_FragColor  = colorLeft;
 }
 }
 else if(sCurrentGLControl==3) 
 { 
  if ( vTexCoord.x <=leftsliderDelta )
 {
  vec4 colorRight=texture2D (sTexture_2, vec2((vTexCoord.x)+leftsliderStartval, vTexCoord.y+sSelectedRightEndVerticalShift));
   //i want to show this result in a projected view like glcontrol2
    gl_FragColor  = colorRight;  
   }
  }

else if(sCurrentGLControl==2) 
 {  //Projection works fine 
vec2  pos     = vTexCoord.xy * 2.0 - 1.0;
float b       = 0.3;
float v_scale = (1.0 + b) / (1.0 + b * sqrt(1.0 - pos.x*pos.x));
float u = asin( pos.x ) / 3.1415 + 0.5;
float v = (pos.y * v_scale) * 0.5 + 0.5;
if ( v < 0.0 || v > 1.0 )
  discard;
vec3 texColor = texture2D( sTexture_1, vec2(u, v) ).rgb;
gl_FragColor  = vec4( texColor.rgb, 1.0 );   
  }
    }");

  ==================================================================
if (glControl.Name == "glControl1")
        {
            GL.Viewport(new Rectangle(-glControl.Width, 0, glControl.Width*2.0, glControl.Height));

        }
        else if (glControl.Name == "glControl2")
        {
            GL.Viewport(new Rectangle(0, 0, glControl.Width , glControl.Height));

        }
        else
        {
            GL.Viewport(new Rectangle(0, 0, glControl.Width*2.0, glControl.Height));

        }

Answer 1

如果你不想扭曲“丢弃”区域，只需保留原始纹理坐标即可：

precision highp float;

uniform sampler2D sTexture;
varying vec2 vTexCoordIn;

void main ()
{
    vec2 uv = vTexCoordIn.xy

    if (vTexCoordIn.x >= 0.7 && vTexCoordIn.x <= 0.9)
    {
        vec2  pos     = vTexCoordIn.xy * 2.0 - 1.0;
        float b       = 0.3;
        float v_scale = (1.0 + b) / (1.0 + b * sqrt(1.0 - pos.x*pos.x));

        float u = asin( pos.x ) / 3.1415 + 0.5;
        float v = (pos.y * v_scale) * 0.5 + 0.5;
        if (v >= 0.0 && v <= 1.0)
          uv = vec2(u, v);
    }

    vec3 texColor = texture2D(sTexture, uv).rgb;
    gl_FragColor  = vec4(texColor.rgb, 1.0);
}

---

根据问题的变化进行编辑：

如果您只想显示纹理的一部分，那么您必须在查找纹理时将纹理坐标从范围 [0, 1] 映射到范围 [left, right]：

u = u * rightsliderDelta + rightsliderStartval;  
vec3 texColor = texture2D( sTexture_2, vec2(u, v) ).rgb;

将其应用到您的代码中，如下所示：

例如：

void main ()
{
    vec2 vTexCoord=vec2(vTexCoordIn.x,vTexCoordIn.y);

    float rightsliderStartval=sSelectedRangeRight;//0.5(value between 0.5 and 1.0)
    float rightsliderEndval=sSelectedRangeRightEnd;//1.0(value between 0.5 and 1.0)
    float rightsliderDelta=rightsliderEndval-rightsliderStartval;

    // [...]

    if(sCurrentGLControl==1) {

        vec2  pos     =  vTexCoord.xy * 2.0 - 1.0;
        float b       = 0.3;
        float v_scale = (1.0 + b) / (1.0 + b * sqrt(1.0 - pos.x*pos.x));
        float u = asin( pos.x ) / 3.1415 + 0.5;
        float v = (pos.y * v_scale) * 0.5 + 0.5;
        if ( v < 0.0 || v > 1.0 )
            discard;

        u = u * rightsliderDelta + rightsliderStartval;   
        vec3 colorLeft = texture2D( sTexture_2, vec2(u, v) ).rgb;
        gl_FragColor   = vec4( colorLeft .rgb, 1.0 );
    }

    // [...]

}