glReadPixels() “数据"参数用法? [英] glReadPixels() "data" argument usage?

问题描述

我正在尝试使用 glReadPixels 从图像中获取颜色数据.我应该使用 glReadPixels 但我似乎无法弄清楚.这是一个更大项目的一部分，但现在我只想知道如何正确使用它.

I'm trying to use glReadPixels to get color data from an image. I'm supposed to be using glReadPixels but I can't seem to figure it out. It's part of a much larger project, but right now all I want is to know how to properly use this.

我查了一下，结果是这样的:

I looked it up and got something like this:

    void glReadPixels(GLint x, 
       GLint y, 
       GLsizei width, 
       GLsizei height, 
       GLenum format, 
       GLenum type, 
       GLvoid* data);

但我不确定我应该把什么作为最后一个论点，当我这样做时，我什至会如何使用它.帮助将不胜感激！(即:如何使用它或如何获取颜色的简单示例)

But I'm not sure what I should be putting in as that last argument, and when I do, how I would even use it. Help would really be appreciated! (ie: a simple example of how to use it, or how to get the color)

推荐答案

data 接受一个指向您为 glReadPixels 准备将数据放入的缓冲区的指针.像这样:

data takes a pointer to some buffer you prepared for glReadPixels to put the data into. Like this:

switch(format) {
case GL_BGR:
case GL_RGB:
    components = 3; break;

case GL_BGRA:
case GL_RGBA:
    components = 4; break;

case GL_ALPHA:
case GL_LUMINANCE:
    components = 1; break;
}

GLubyte *data = malloc(components * width * height);
if( data ) {
    glReadPixels(0, 0, width, height, format, GL_UNSIGNED_BYTE, data);
}

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