在OpenGL ES（iPhone）中绘制到屏幕外渲染缓冲区 [英] Draw to offscreen renderbuffer in OpenGL ES (iPhone)

问题描述

我正在尝试在iPhone上的OpenGL ES中创建一个屏幕外渲染缓冲区。我已经创建了这样的缓冲区：

I'm trying to create an offscreen render buffer in OpenGL ES on the iPhone. I've created the buffer like this:

        glGenFramebuffersOES(1, &offscreenFramebuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, offscreenFramebuffer);

    glGenRenderbuffersOES(1, &offscreenRenderbuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, offscreenRenderbuffer);
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, offscreenRenderbuffer);

但我对如何渲染存储感到困惑。 Apple的文档说要使用EAGLContext renderBufferStorage：fromDrawable：方法，但这似乎只适用于一个渲染缓冲区（显示的主渲染缓冲区）。如果我使用普通的OpenGL函数glRenderBufferStorageOES，那么我似乎无法让它显示出来。这是代码：

But I'm confused on how to render the storage. Apple's documentation says to use the EAGLContext renderBufferStorage:fromDrawable: method, but this seems to only work for one render buffer (the main one being displayed). If I use the normal OpenGL function glRenderBufferStorageOES, then I can't seem to get it to display. Here's the code:

        // this is in the initialization section:
    glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGB8_OES, backingWidth, backingHeight);

    // and this is when I'm trying to draw to it and display it:
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, offscreenFramebuffer);
    GLfloat vc[] = {
        0.0f, 0.0f, 0.0f,
        10.0f, 10.0f, 10.0f,
        0.0f, 0.0f, 0.0f,
        -10.0f, -10.0f, -10.0f,         
    };

    glLoadIdentity();
    glEnableClientState(GL_VERTEX_ARRAY);
    glVertexPointer(3, GL_FLOAT, 0, vc);
    glDrawArrays(GL_LINES, 0, 4);
    glDisableClientState(GL_VERTEX_ARRAY);

    glBindRenderbufferOES(GL_RENDERBUFFER_OES, offscreenRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

这样做，屏幕上不显示任何内容。但是，如果我将对offscreen ... Buffer的引用切换到使用renderBufferStorage方法创建的缓冲区，则它可以正常工作。

Doing it this way, nothing is displayed on the screen. However, if I switch out the references to "offscreen...Buffer" to the buffers that were created with the renderBufferStorage method, it works fine.

有任何建议吗？ / p>

Any suggestions?

推荐答案

@david好主意..你需要做的是@prideout说的......创建一个纹理并渲染它。并且每次都使用四边形上的纹理。确保你只绘制一次纹理，就像你的情况一样持久。

@david good idea.. what you need to do is what @prideout said.. create a texture and render to it.. and use the texture on a quad every time. Make sure you draw to the texture only once, as in your case things are persistent.

- (void)setUpTextureBuffer 
{
 glGenFramebuffersOES(1, &texturebuffer); 
 glBindFramebufferOES(GL_FRAMEBUFFER_OES, texturebuffer);

 // create the texture
 glGenTextures(1, &canvastexture); 
 glBindTexture(GL_TEXTURE_2D, canvastexture); 
 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); 
 glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, canvastexture, 0);

 GLenum status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES); 
 if(status != GL_FRAMEBUFFER_COMPLETE_OES) { 
  NSLog(@"failed to make complete framebuffer object %x", status);
 }

 glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
 glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

 glClearColor(1.0, 1.0, 1.0, 1.0);
 glViewport(0, 0, 512, 512);
 glClear(GL_COLOR_BUFFER_BIT);
}



//setTargetToTexture() function

 glBindFramebufferOES(GL_FRAMEBUFFER_OES, tbuffer);
 glBindTexture(GL_TEXTURE_2D, allbrushes);
 glViewport(0, 0, 512, 512);

//reset pointers after finishing drawing to textures

 glViewport(0, 0, BWIDTH, BHEIGHT);
 glVertexPointer(2, GL_FLOAT, 0, canvas);   //canvas vertices
 glTexCoordPointer(2, GL_FLOAT, 0, texels);
 glBindTexture(GL_TEXTURE_2D, boundtexture);   //bind to the texture which is the special render target 
 glBindFramebufferOES(GL_FRAMEBUFFER_OES, fbuffer); //back to normal framebuffer

这篇关于在OpenGL ES（iPhone）中绘制到屏幕外渲染缓冲区的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！