如何从图像的顶部和底部 hide/remove 特定区域 - GLControl

Question

我可以在 glControl 中使用 opengl 显示下图。有什么方法可以从 glControl 的底部和顶部均等地剪切或隐藏特定区域（比如从顶部和底部 50px）？下面是我用来计算 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

如果你想跳过纹理的某些部分，那么你可以使用discard关键字。此命令导致片段的输出值被丢弃，并且根本不绘制片段。

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;
}

如果给定图片的高度和需要舍弃的区域的高度，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;

如何从图像的顶部和底部 hide/remove 特定区域 - GLControl

How to hide/remove particular area from top and bottom of image - GLControl

c#

opengl

shader

glsl

opentk