如何从图像的顶部和底部隐藏/删除特定区域-GLControl

Question

我可以在glControl中使用opengl在图像下方显示。有什么方法可以从glControl的底部和顶部平等地切割或隐藏特定区域（例如，顶部和底部距50px）？以下是我用来计算glControl大小的代码。我可以通过更改视口上的值来实现吗？

private void OpenGL_Size(GLControl glControl, VideoCaptureDevice videoSource)//always in portrait  mode

{
    decimal RateOfResolution = (decimal)videoSource.VideoResolution.FrameSize.Width / (decimal)videoSource.VideoResolution.FrameSize.Height;

    decimal screenHeightbyTwo = this._Screenheight / 2;             
    RateOfResolution = 1 / RateOfResolution;// portrait 
    openGLheight = Convert.ToInt32(screenHeightbyTwo);   // height is fixed; calculate the width
    openGLwidth = (Convert.ToInt32(RateOfResolution * screenHeightbyTwo));

    glControl.Width = openGLwidth;
    glControl.Height = openGLheight;
}

GL.Viewport(new Rectangle(0, 0, glControl.Width, glControl.Height));

着色器代码

precision highp float;
uniform sampler2D sTexture;
varying vec2 vTexCoordIn;
void main ()
{ 
    vec4 color = texture2D(sTexture,vTexCoordIn);
    gl_FragColor = color;
}

Answer 1

如果要跳过纹理的某些部分，则可以使用discard关键字。此命令将导致片段的输出值被丢弃，并且根本不会绘制片段。

precision highp float;

uniform sampler2D sTexture;
varying vec2 vTexCoordIn;

void main ()
{ 
    if (vTexCoordIn.y < 0.1 || vTexCoordIn.y > 0.9)
        discard;

    vec4 color = texture2D(sTexture, vTexCoordIn);
    gl_FragColor = color;
}

如果给出了图像的高度和必须丢弃的区域的高度，则条件为：

float img_h_px  = 432.0; // height of the image in pixel
float area_h_px = 50.0;  // area height in pixel

float w = area_h_px/img_h_px;
if (vTexCoordIn.y < w || vTexCoordIn.y > (1.0-w))
    discard;