I want to use function glReadPixels() to do screenshot of my scene. And it works great if I don't use multisampling. But if I do I get GL_INVALID_OPERATION in glResolveMultisampleFramebufferAPPLE(). Is there a way to resolve this problem?
My save function:
var wid = GLint()
var hei = GLint()
glGetRenderbufferParameteriv(GLenum(GL_RENDERBUFFER), GLenum(GL_RENDERBUFFER_WIDTH), &wid)
glGetRenderbufferParameteriv(GLenum(GL_RENDERBUFFER), GLenum(GL_RENDERBUFFER_HEIGHT), &hei)
let byteLength = Int(hei * wid) * 4
let bytes = UnsafeMutablePointer<GLubyte>.alloc(byteLength)
// init non-multisampled frame buffer
var framebuffer: GLuint = 0
var colorRenderbuffer: GLuint = 0
glGenFramebuffersOES(1, &framebuffer)
glBindFramebufferOES(GLenum(GL_FRAMEBUFFER_OES), framebuffer)
glGenRenderbuffersOES(1, &colorRenderbuffer)
glBindRenderbufferOES(GLenum(GL_RENDERBUFFER_OES), colorRenderbuffer)
glRenderbufferStorageOES(GLenum(GL_RENDERBUFFER_OES), GLenum(GL_RGBA8_OES), wid, hei)
glFramebufferRenderbufferOES(GLenum(GL_FRAMEBUFFER_OES), GLenum(GL_COLOR_ATTACHMENT0_OES), GLenum(GL_RENDERBUFFER_OES), colorRenderbuffer)
glBindFramebufferOES(GLenum(GL_DRAW_FRAMEBUFFER_APPLE), framebuffer)
var default: GLint = 0
glGetIntegerv(GLenum(GL_FRAMEBUFFER_BINDING_OES), &default)
glBindFramebufferOES(GLenum(GL_READ_FRAMEBUFFER_APPLE), GLuint(default));
myglGetError() // OK
glResolveMultisampleFramebufferAPPLE()
myglGetError() // GL_INVALID_OPERATION
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), framebuffer)
glReadPixels(0, 0, GLsizei(wid), GLsizei(hei), GLenum(GL_RGBA), GLenum(GL_UNSIGNED_BYTE), bytes)
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), GLuint(default));
glDeleteFramebuffers(1, &framebuffer)
I use default frame buffer initialized by GLKit with glkView.drawableMultisample = GLKViewDrawableMultisample.Multisample4X
I have tried your sample and it seems that after some modifications it works. Modificated code:
var wid = GLint()
var hei = GLint()
glGetRenderbufferParameteriv(GLenum(GL_RENDERBUFFER), GLenum(GL_RENDERBUFFER_WIDTH), &wid)
glGetRenderbufferParameteriv(GLenum(GL_RENDERBUFFER), GLenum(GL_RENDERBUFFER_HEIGHT), &hei)
var def: GLint = 0
glGetIntegerv(GLenum(GL_FRAMEBUFFER_BINDING_OES), &def)
// init non-multisampled frame buffer
var framebuffer: GLuint = 0
var colorRenderbuffer: GLuint = 0
glGenFramebuffersOES(1, &framebuffer)
glBindFramebufferOES(GLenum(GL_FRAMEBUFFER_OES), framebuffer)
glGenRenderbuffersOES(1, &colorRenderbuffer)
glBindRenderbufferOES(GLenum(GL_RENDERBUFFER_OES), colorRenderbuffer)
glRenderbufferStorageOES(GLenum(GL_RENDERBUFFER_OES), GLenum(GL_RGBA8_OES), wid, hei)
glFramebufferRenderbufferOES(GLenum(GL_FRAMEBUFFER_OES), GLenum(GL_COLOR_ATTACHMENT0_OES), GLenum(GL_RENDERBUFFER_OES), colorRenderbuffer)
glBindFramebufferOES(GLenum(GL_DRAW_FRAMEBUFFER_APPLE), framebuffer)
//commented
//here GL_FRAMEBUFFER_BINDING_OES will be overrided by previous call of
// 'glBindRenderbufferOES(GLenum(GL_RENDERBUFFER_OES), colorRenderbuffer)'
//var def: GLint = 0
//glGetIntegerv(GLenum(GL_FRAMEBUFFER_BINDING_OES), &def
glBindFramebufferOES(GLenum(GL_READ_FRAMEBUFFER_APPLE), GLuint(def));
var err = glGetError()
print(String(format: "Error %X", err))
glResolveMultisampleFramebufferAPPLE()
err = glGetError()
print(String(format: "Error %X", err)) // GL_INVALID_OPERATION
glBindFramebuffer(GLenum(GL_FRAMEBUFFER), framebuffer)
Also here is quote from APPLE_framebuffer_multisample.txt extension description which explains why modified code works, as far as I understand.
Calling BindFramebuffer with set to FRAMEBUFFER binds the framebuffer to both DRAW_FRAMEBUFFER_APPLE and READ_FRAMEBUFFER_APPLE.