glClear() doesn't work on some machines - macos

Question

I've got an OpenGL context with an FBO and all of my simple drawing operations work fine except for glClear(). I can draw textures and rectangles but glClear() refuses to do anything. glGetError() does not return any error.
Im calling glClear() like this:
glRectd(0, 0, 1024, 1080); // I see the results of this call
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // This does nothing
Note that this code with glClear() works fine on some Macs but not on others so perhaps I've been getting lucky and I need to setup the context or some other setting differently. Any suggestions would be greatly appreciated!
Edit: This has something to do with drawing the texture from the FBO onto another context. After that happens, glClear() stops working.
Edit 2: I now have it reproduced in a small Xcode project and I'm pretty sure I've concluded that everything works on the NVIDIA card but not on the integrated Intel Iris card. I'll post the test code shortly.
Edit 3: Code. I tried to minimize it but there's still a bit of bulk.
//
// On the NVIDIA card, we'll see the video switch between red and green.
// On the Intel Iris, it will get stuck on blue because of "break" code below.
//
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
// Initialize the view to white
[self clearContext:_view.openGLContext.CGLContextObj toRed:1 green:1 blue:1 alpha:1];
// FBO context
fbo = [[WTFBOContext alloc] initWithWidth:_view.frame.size.width height:_view.frame.size.height shareContext:_view.openGLContext];
// Clear the FBO context (and thus texture) to solid blue
[self clearContext:fbo.oglCtx.CGLContextObj toRed:0 green:0 blue:1 alpha:1];
// These calls "break" the FBO on Intel Iris chips
{
CGLContextObj cgl_ctx = _view.openGLContext.CGLContextObj;
glEnable(GL_TEXTURE_RECTANGLE_EXT);
glBindTexture(GL_TEXTURE_RECTANGLE_EXT, fbo.texture);
glBegin(GL_QUADS);
glEnd();
}
__block int r = 0;
[NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
r = 1 - r;
// Clear the FBO context (and thus texture) to solid red or green
[self clearContext:fbo.oglCtx.CGLContextObj toRed:r green:1 - r blue:0 alpha:1];
[self drawTexture:fbo.texture
fromRect:_view.frame
toContext:_view.openGLContext.CGLContextObj
inRect:_view.frame
flipped:NO
mirrored:NO
blending:NO
withAlpha:1.0];
}];
}
- (void) clearContext:(CGLContextObj) cgl_ctx
toRed:(GLfloat) red
green:(GLfloat) green
blue:(GLfloat) blue
alpha:(GLfloat) alpha
{
glClearColor(red, green, blue, alpha);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glFlush();
}
- (void) drawTexture:(GLuint) tname
fromRect:(CGRect) fromRect
toContext:(CGLContextObj) cgl_ctx
inRect:(CGRect) inRect
flipped:(BOOL) flipped
mirrored:(BOOL) mirrored
blending:(BOOL) blending
withAlpha:(GLfloat) withAlpha
{
glEnable(GL_TEXTURE_RECTANGLE_EXT);
glBindTexture(GL_TEXTURE_RECTANGLE_EXT, tname);
GLint vp[4];
glGetIntegerv(GL_VIEWPORT, vp);
GLdouble left, right, bottom, top;
if (flipped)
{
bottom = vp[1] + vp[3];
top = vp[1];
}
else
{
bottom = vp[1];
top = vp[1] + vp[3];
}
if (mirrored)
{
left = vp[0] + vp[2];
right = vp[0];
}
else
{
left = vp[0];
right = vp[0] + vp[2];
}
glMatrixMode (GL_PROJECTION);
glPushMatrix();
glLoadIdentity ();
glOrtho (left, right, bottom, top, -1, 1);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
GLboolean wasBlending = glIsEnabled(GL_BLEND);
if (blending)
{
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
}
else
glDisable(GL_BLEND);
// Texures are multiplied by the current color.
glColor4f(withAlpha, withAlpha, withAlpha, withAlpha);
glBegin(GL_QUADS);
glTexCoord2f(fromRect.origin.x, fromRect.origin.y);
glVertex2i(inRect.origin.x, inRect.origin.y);
glTexCoord2f(fromRect.origin.x, fromRect.origin.y + fromRect.size.height);
glVertex2i(inRect.origin.x, inRect.origin.y + inRect.size.height);
glTexCoord2f(fromRect.origin.x + fromRect.size.width, fromRect.origin.y + fromRect.size.height);
glVertex2i(inRect.origin.x + inRect.size.width, inRect.origin.y + inRect.size.height);
glTexCoord2f(fromRect.origin.x + fromRect.size.width, fromRect.origin.y);
glVertex2i(inRect.origin.x + inRect.size.width, inRect.origin.y);
glEnd();
glMatrixMode (GL_PROJECTION);
glPopMatrix();
if (wasBlending)
glEnable(GL_BLEND);
else
glDisable(GL_BLEND);
glFlush();
glBindTexture(GL_TEXTURE_RECTANGLE_EXT, 0);
}
Support Files:
#interface WTFBOContext : NSObject
{
GLuint framebuffer;
}
#property (nonatomic, retain) NSOpenGLContext *oglCtx;
#property (nonatomic, retain) NSOpenGLPixelFormat *oglFmt;
#property (nonatomic) GLuint texture;
#property (nonatomic, readonly) NSUInteger width;
#property (nonatomic, readonly) NSUInteger height;
- (id)initWithWidth:(NSUInteger)width height:(NSUInteger)height shareContext:(NSOpenGLContext *)shareContext;
// We take ownership of the texture
- (void)setTexture:(GLuint)texture;
- (BOOL)isComplete;
#end
#implementation WTFBOContext
- (id)initWithWidth:(NSUInteger)width height:(NSUInteger)height shareContext:(NSOpenGLContext *)shareContext
{
self = [super init];
_width = width;
_height = height;
NSOpenGLPixelFormatAttribute attributes[] = {
NSOpenGLPFANoRecovery,
NSOpenGLPFAAccelerated,
NSOpenGLPFADepthSize, (NSOpenGLPixelFormatAttribute)24,
(NSOpenGLPixelFormatAttribute)0};
self.oglFmt = [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes];
self.oglCtx = [[NSOpenGLContext alloc] initWithFormat:self.oglFmt shareContext:shareContext];
CGLContextObj cgl_ctx = self.oglCtx.CGLContextObj;
glGenFramebuffersEXT(1, &framebuffer);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer);
[self _makeTexture];
glViewport(0, 0, _width, _height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, _width, 0, _height, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
return self;
}
- (void)dealloc
{
CGLContextObj cgl_ctx = self.oglCtx.CGLContextObj;
glDeleteTextures(1, &_texture);
}
- (void)_makeTexture
{
CGLContextObj cgl_ctx = self.oglCtx.CGLContextObj;
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_RECTANGLE_EXT, texture);
glTexParameteri(GL_TEXTURE_RECTANGLE_EXT, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_RECTANGLE_EXT, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_RECTANGLE_EXT, 0, GL_RGBA8, _width, _height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
self.texture = texture;
}
- (void)setTexture:(GLuint)tex
{
CGLContextObj cgl_ctx = self.oglCtx.CGLContextObj;
if (_texture > 0)
glDeleteTextures(1, &_texture);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_EXT, tex, 0);
if (!self.isComplete)
NSLog(#"glFramebufferTexture2DEXT");
_texture = tex;
}
- (BOOL)isComplete
{
CGLContextObj cgl_ctx = self.oglCtx.CGLContextObj;
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, framebuffer);
GLuint status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
return status == GL_FRAMEBUFFER_COMPLETE_EXT;
}
#end