使用framebuffer来渲染纹理总是会产生白色的纹理。

Using a couple of posts here in *, I created what is supposed to be a simple render-to-texture using a framebuffer.

在*中使用了几个帖子，我使用framebuffer创建了一个简单的renderto -纹理。

The problem here is that it's not working. Something is broken in the mix, as my final texture is just a white square. I am not getting any gl errors whatsoever. Here is my code.

这里的问题是它不起作用。我最终的纹理只是一个白色的正方形，所以在混合中有一些东西被打破了。我不会得到任何gl错误。这是我的代码。

Declare instance variables.

声明实例变量。

GLuint texture;
GLuint textureFrameBuffer;

Generate the texture and framebuffer.

生成纹理和框架缓冲区。

    glGetError();

    //Generate the texture that we will draw to (saves us a lot of processor).
    glEnable(GL_TEXTURE_2D);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    // Use OpenGL ES to generate a name for the texture.
    // Pass by reference so that our texture variable gets set.
    glGenTextures(1, &texture);

    // Bind the texture name. 
    glBindTexture(GL_TEXTURE_2D, texture);

    // Specify a 2D texture image, providing a pointer to the image data in memory.
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 128, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

    //Create a frame buffer to draw to. This will allow us to directly edit the texture.
    GLint oldFBO;
    glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, &oldFBO);
    glGenFramebuffersOES(1, &textureFrameBuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, textureFrameBuffer);
    glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, texture, 0);

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, oldFBO);

    GLenum err = glGetError();
    if (err != GL_NO_ERROR)
    {
        NSLog(@"Error on framebuffer init. glError: 0x%04X", err);
    }

Draw a big string into the framebuffer.

在framebuffer中绘制一个大字符串。

glGetError();

GLint oldFBO;
glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, &oldFBO);

//Bind our frame buffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, textureFrameBuffer);

//Clear out the texture.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

//Draw the letters to the frame buffer. (calls glDrawArrays a bunch of times, binds various textures, etc.) Does everything in 2D.
[self renderDialog:displayString withSprite:displaySprite withName:displaySpriteName];

//Unbind the frame buffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, oldFBO);

GLenum err = glGetError();
if (err != GL_NO_ERROR)
{
    NSLog(@"Error on string creation. glError: 0x%04X", err);
}

Draw it.

画出来。

    glColor4f(1.0f, 1.0f, 1.0f, 1.0f);

    glGetError();

    //Draw the text.
    [EAGLView enable2D];

    //Push the matrix so we can keep it as it was previously.
    glPushMatrix();

    //Store the coordinates/dimensions from the rectangle.
    float x = 0;
    float y = [Globals getPlayableHeight] - dialogRect.size.height;
    float w = [Globals getPlayableWidth];
    float h = dialogRect.size.height;

    // Set up an array of values to use as the sprite vertices.
    GLfloat vertices[] =
    {
        x,      y,
        x,      y+h,
        x+w,    y+h,
        x+w,    y
    };

    // Set up an array of values for the texture coordinates.
    GLfloat texcoords[] =
    {
        0,          0,
        0,          h / 128,
        w / 512,    h / 128,
        w / 512,    0
    };

    //Render the vertices by pointing to the arrays.
    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glTexCoordPointer(2, GL_FLOAT, 0, texcoords);

    // Set the texture parameters to use a linear filter when minifying.
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    //Allow transparency and blending.
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    //Enable 2D textures.
    glEnable(GL_TEXTURE_2D);

    //Bind this texture.
    [EAGLView bindTexture:texture];

    //Finally draw the arrays.
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

    //Restore the model view matrix to prevent contamination.
    glPopMatrix();

    GLenum err = glGetError();
    if (err != GL_NO_ERROR)
    {
        NSLog(@"Error on draw. glError: 0x%04X", err);
    }

Any external things I called work just fine in other contexts. Any ideas? I know almost nothing about framebuffers, so any help troubleshooting would be great.

我所说的任何外部事物在其他情况下都可以工作。什么好主意吗?我对framebuffer几乎一无所知，因此任何帮助故障排除都是很好的。

1 个解决方案

#1

Texture parameters are set on a per-texture basis. The code you posted appears to be setting GL_TEXTURE_MIN_FILTER before the texture you’re rendering to has been created or bound. If you’re not setting the filter anywhere else, and you haven’t specified texture images for the remaining levels, your texture is likely incomplete, which is why you’re getting white.

纹理参数是根据纹理设置的。在创建或绑定要呈现的纹理之前，您所发布的代码似乎正在设置GL_TEXTURE_MIN_FILTER。如果您没有在其他地方设置过滤器，并且没有为其余的级别指定纹理图像，那么您的纹理很可能是不完整的，这就是为什么您会得到白色。

For future reference, the absence of GL errors after framebuffer setup does not mean that the framebuffer is usable for rendering. You should also check that the framebuffer is complete by calling glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) and verifying that GL_FRAMEBUFFER_COMPLETE_OES is returned.

对于将来的参考，在framebuffer设置之后没有GL错误并不意味着framebuffer可以用于渲染。您还应该通过调用glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES)并验证是否返回了GL_FRAMEBUFFER_COMPLETE_OES来检查framebuffer是否完整。