ios - 为什么多重采样不起作用？

Question

我正在尝试让多重采样在我的 OpenGL ES 应用程序中工作。

帧缓冲区设置代码:

glGenFramebuffersOES(1, &framebuffer);
glGenRenderbuffersOES(1, &colorRenderbuffer);

glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);  
glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(id<EAGLDrawable>)self.layer];
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorRenderbuffer);

GLint backingWidth;
GLint backingHeight;
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);

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

glGenRenderbuffersOES(1, &sampleColorRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, sampleColorRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_RGBA8_OES, backingWidth, backingWidth);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, sampleColorRenderbuffer);

glGenRenderbuffersOES(1, &sampleDepthRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, sampleDepthRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER_OES, 4, GL_DEPTH_COMPONENT16_OES, backingWidth, backingWidth);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, sampleDepthRenderbuffer);

渲染代码:

glBindFramebufferOES(GL_RENDERBUFFER_OES, sampleFramebuffer);
glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

GLfloat vertices[] = {
    1.0f, 1.0f, 0.0f,
    2.0f, 4.0f, 0.0f,
    1.0f, 3.0f, 0.0f
};
glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
glVertexPointer(3, GL_FLOAT, 0, vertices);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 3);

glBindFramebufferOES(GL_READ_FRAMEBUFFER_APPLE, sampleFramebuffer);
glBindFramebufferOES(GL_DRAW_FRAMEBUFFER_APPLE, framebuffer);
glResolveMultisampleFramebufferAPPLE();

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

结果:

如您所见，三角形的边仍然有锯齿。

Answer 1

sampleFramebuffer 是 framebuffer，不是 renderbuffer。但是您在渲染代码中将其绑定(bind)为渲染缓冲区。那是错误的。您应该通过调用 glGetError 检查 OpenGL 错误 - 它会告诉您哪个 GL 调用无效。

您的渲染代码应以以下行开头:

glBindFramebufferOES(GL_FRAMEBUFFER_OES, sampleFramebuffer);

其他都还好。但是为了提高性能，您可以在 Resolve 调用后对多重采样帧缓冲区使用 glDiscardFramebufferEXT 调用:

glResolveMultisampleFramebufferAPPLE();
const GLenum discards[]  = {GL_COLOR_ATTACHMENT0,GL_DEPTH_ATTACHMENT};
glDiscardFramebufferEXT(GL_READ_FRAMEBUFFER_APPLE,2,discards);