glResolveMultisampleFramebufferAPPLE() génère GL_INVALID_OPERATION sur iOS (OpenGL ES 2.0)

Question

Je souhaite utiliser la fonction glReadPixels() pour faire une capture d'écran de ma scène. Et cela fonctionne très bien si je n'utilise pas le multi-échantillonnage. Mais si je le fais, je reçois GL_INVALID_OPERATION en glResolveMultisampleFramebufferAPPLE(). Y a-t-il un moyen de résoudre ce problème?

Ma fonction d'économie:

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) 

J'utilise un tampon de trame par défaut initialisé par GLKit avec glkView.drawableMultisample = GLKViewDrawableMultisample.Multisample4X

Answer 1

J'ai essayé votre échantillon et il semble que, après quelques modifications, il fonctionne. Code Modificated:

 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) 

Aussi voici la description citation de APPLE_framebuffer_multisample.txt d'extension qui explique pourquoi le code modifié fonctionne, pour autant que je comprends.

Calling BindFramebuffer with set to FRAMEBUFFER binds the framebuffer to both DRAW_FRAMEBUFFER_APPLE and READ_FRAMEBUFFER_APPLE.

APPLE_framebuffer_multisample