FBO中如何使用模板缓冲区

时间：2021-12-08 05:00:33

FBO常用框架

一般需求只有color buffer，depth buffer，前者一般用纹理，后者一般用rbo。标准程序如下： 
// 创建
// frame buffer object
glGenFramebuffers(1, &fboId);
glBindFramebuffer(GL_FRAMEBUFFER, fboId);

// color buffer with texture object
glGenTextures(1, &color_rboId);
glBindTexture(GL_TEXTURE_2D, color_rboId);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, targetWidth, targetHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

// depth buffer with render buffer object
glGenRenderbuffers(1, &depth_rboId);
glBindRenderbuffer(GL_RENDERBUFFER, depth_rboId);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, targetWidth, targetHeight);

// Attach color buffer to FBO
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color_rboId, 0);

//Attach depth buffer to FBO
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth_rboId);


//Also attach as a stencil
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depth_stencil_rb);

// 删除
if (fboId != 0)
{
glDeleteFramebuffers(1, &fboId);
fboId = 0;
}

if (depth_rboId != 0)
{
glDeleteRenderbuffers(1, &depth_rboId);
depth_rboId = 0;
}

if (color_rboId)
{
glDeleteTextures(1, &color_rboId);
color_rboId = 0;
}

FBO中如何增加stencil buffer

 正常人都会认为stencil buffer 跟depth buffer类似，于是乎写出一套类似depth buffer的框架： 
// 创建stencil buffer以RBO形式
glGenRenderbuffers(1, &stencil_rboId);
glBindRenderbuffer(GL_RENDERBUFFER, stencil_rboId);
glRenderbufferStorage(GL_RENDERBUFFER, GL_STENCIL_INDEX, targetWidth, targetHeight);

// 关联stencil buffer 和FBO
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, stencil_rboId);

// 删除stencil buffer
glDeleteRenderbuffers(1, &stencil_rboId);
但实际测试，发现stencil buffer根本不起作用，下面是一个测试函数：
void stencilRenderTest()
{
GLdouble dRadius = 0.1; // Initial radius of spiral
GLdouble dAngle;        // Looping variable
float x = 100;
float y = 100;
float rsize = 25;

// Clear blue window
glClearColor(0.0f, 0.0f, 1.0f, 0.0f);

// Use 0 for clear stencil, enable stencil test
glClearStencil(0.0f);
glEnable(GL_STENCIL_TEST);

// Clear color and stencil buffer
glClear(GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

// All drawing commands fail the stencil test, and are not
// drawn, but increment the value in the stencil buffer. 
glStencilFunc(GL_NEVER, 0x0, 0x0);
glStencilOp(GL_INCR, GL_INCR, GL_INCR);

// Spiral pattern will create stencil pattern
// Draw the spiral pattern with white lines. We 
// make the lines  white to demonstrate that the 
// stencil function prevents them from being drawn
glColor3f(1.0f, 1.0f, 1.0f);
glBegin(GL_LINE_STRIP);
for(dAngle = 0; dAngle < 400.0; dAngle += 0.1)
{
glVertex2d(dRadius * cos(dAngle), dRadius * sin(dAngle));
dRadius *= 1.002;
}
glEnd();

// Now, allow drawing, except where the stencil pattern is 0x1
// and do not make any further changes to the stencil buffer
glStencilFunc(GL_NOTEQUAL, 0x1, 0x1);
glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);

// Now draw red bouncing square
// (x and y) are modified by a timer function
glColor3f(1.0f, 0.0f, 0.0f);
glRectf(x, y, x + rsize, y - rsize);

}
stencil正确时，结果显示是一个蓝色背景，红色小矩形块，矩形内部可以看到圆弧，下图右。stencil不正确结果是蓝色背景同心圆环 以及一个矩形红色块，图左。FBO中如何使用模板缓冲区

FBO中正确使用stencil buffer

 在官方wiki教程中找到答案：

EVER EVER MAKE A STENCIL buffer. All GPUs and all drivers do not support an independent stencil buffer. If you need a stencil buffer, then you need to make a Depth=24, Stencil=8 buffer, also called D24S8. Please search for the example about GL_EXT_packed_depth_stencil on this page.
翻译过来就是：永远不要单独创建一个模板缓冲区，所有的gpu和驱动都不支持单独的模板缓冲区。如果需要创建模板缓冲时 需要深度、模板共用一个缓冲区，格式是DEPTH_24_STENCIL_8。

具体code如下：

// 创建
// frame buffer object
glGenFramebuffers(1, &fboId);
glBindFramebuffer(GL_FRAMEBUFFER, fboId);

// color buffer with texture object
glGenTextures(1, &color_rboId);
glBindTexture(GL_TEXTURE_2D, color_rboId);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, targetWidth, targetHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

// depth buffer and stencil buffer
glGenRenderbuffers(1, &depth_stencil_rb);
glBindRenderbuffer(GL_RENDERBUFFER, depth_stencil_rb);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, targetWidth, targetHeight); // not GL_DEPTH_COMPONENT24 but GL_DEPTH24_STENCIL8

// Attach color buffer to FBO
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color_rboId, 0);

//Attach depth buffer to FBO
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth_stencil_rb);
//Also attach as a stencil
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depth_stencil_rb);

// 删除
if (fboId != 0)
{
glDeleteFramebuffers(1, &fboId);
fboId = 0;
}

if (depth_stencil_rb != 0)
{
glDeleteRenderbuffers(1, &depth_stencil_rb);
depth_stencil_rb = 0;
}

if (color_rboId)
{
glDeleteTextures(1, &color_rboId);
color_rboId = 0;
}

参考

opengl 官方wiki：https://www.opengl.org/wiki/Framebuffer_Object_Examples

history:

1. 2013/8/14 fix 正确创建fbo帧缓冲区的bug，renderbuffer格式应该是GL_DEPTH24_STENCIL8而不是 GL_DEPTH_COMPONENT24。


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