"MouseDragged" but NSOpenGlView not refreshed until "MouseUp"

Question

I have a curious problem about an App which MainView is inherited from NSOpenGlView. I am able to draw many things in it, like a basic OpenGL tutorial.... but when I try to implement a basic trackball, it looks like the app waits until I release the mouse button before it refreshes my view... even if I call directly the "DrawRect" callback from the "MouseDragged" callback, it acts the same. Then, I really can't find out how to do such a basic thing and what is the problem about my solution..

Any idea?

My NSOpenGLVIew has double buffer, and and additional depth buffer. Here are the main messages.

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

- (void)mouseDragged:(NSEvent *)theEvent {

//[[self openGLContext] makeCurrentContext];


float curPos[3], dx, dy, dz;

dx = curPos[0] - lastPos[0];
dy = curPos[1] - lastPos[1];
dz = curPos[2] - lastPos[2];

angle = 90.0 * sqrt(dx*dx + dy*dy + dz*dz);
axis[0] = lastPos[1]*curPos[2] - lastPos[2]*curPos[1];
axis[1] = lastPos[2]*curPos[0] - lastPos[0]*curPos[2];
axis[2] = lastPos[0]*curPos[1] - lastPos[1]*curPos[0];

//glutPostRedisplay();

//[self drawRect:self.bounds]; // different attempts
[self setNeedsDisplay:YES]; //
//[self display]; 

}

#pragma mark Mouse Handling

- (void)mouseDown:(NSEvent *)theEvent {

m_PreviousMouseLoc = [self convertPoint:[theEvent locationInWindow] fromView:nil];
ptov(m_PreviousMouseLoc.x,m_PreviousMouseLoc.y,m_width,m_height,lastPos);

}

    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////



- (void)mouseUp:(NSEvent *)theEvent {

[self setNeedsDisplay:YES];

}


////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////


void ptov(int x, int y, int width, int height, float v[3]){

float a,d;

// project x,y onto  1/2 sphere  centered within width and height
v[0] = (2.0*x - width)/ width;
v[1] = (height - 2.0*y)/ height;
d = sqrt(v[0]*v[0] + v[1]*v[1]);
v[2] = cos((PI/2)*((d < 1.0) ? d : 1.0));
a = 1.0 / sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2]);
v[0] *=a;
v[1] *=a;
v[2] *=a;

}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////


 -(void)prepareOpenGL{

if( ![ self loadGLTextures ] ){
    NSLog(@"Failed to load GL Textures");
}


 GLint swapInt = 1;

 [[self openGLContext] setValues:&swapInt forParameter:NSOpenGLCPSwapInterval];     // set to vbl sync 


//glEnable( GL_TEXTURE_2D );                // Enable texture mapping
glShadeModel( GL_SMOOTH );                // Enable smooth shading
glClearColor( 0.0f, 0.0f, 0.0f, 0.5f );   // Black background
glClearDepth( 1.0f );                     // Depth buffer setup
glEnable(GL_DEPTH_TEST);                                // Enables Depth Testing
    glEnable (GL_BLEND);
glDepthFunc(GL_LEQUAL);                                 // The Type Of Depth Testing To Do
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);  // Really Nice Perspective Calculations

glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); 


glPolygonOffset (1.0f, 1.0f);

firstOccurenceOfDrawRect = NO;


/* // set start values...
rVel[0] = 0.3; rVel[1] = 0.1; rVel[2] = 0.2; 
rAccel[0] = 0.003; rAccel[1] = -0.005; rAccel[2] = 0.004;*/

    [[self window] setAcceptsMouseMovedEvents: YES]; 

glViewport(0, 0, (GLsizei) self.bounds.size.width, (GLsizei) self.bounds.size.height);  
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

 - (void) drawRect: (NSRect) rect
 { 
 ///    if (firstOccurenceOfDrawRect)
//  [self initGL];

 // On charge la matrice de projection pour définir ce que l'on va voir et comment
glMatrixMode(GL_PROJECTION);

// On centre
glLoadIdentity();

// On prend du recul
glOrtho(-1.0f, 1.0f, -1.5f, 1.5f, -10.0f, 10.0f);

// On efface ce qui a été dessiné auparavant
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// On va maintenant définir ce que l'on veut dessiner
glMatrixMode(GL_MODELVIEW);


// Avant de commencer à dessiner, on va affecter de deux rotations le repère des coordonnées du cube pour le faire "bouger"
glLoadIdentity();
glRotatef(angle, axis[0], axis[1], axis[2]); 

//  [self resizeGL]; // forces projection matrix update (does test for size changes)
//  [self updateModelView];

    glColor3f (1.0, 1.0, 1.0); 
    glDisable(GL_CULL_FACE);
    glFrontFace(GL_CW);
    glutSolidTeapot(200.0);
    glFrontFace(GL_CCW);

    glEnable(GL_TEXTURE_2D);

    glBindTexture( GL_TEXTURE_2D, texture[ 0 ] );   // Select our texture

    glBegin( GL_QUADS );
    // Front
    glTexCoord2f( 0.0f, 0.0f );
    glVertex3f( -1.0f, -1.0f,  0.0f );   // Bottom left
    glTexCoord2f( 1.0f, 0.0f );
    glVertex3f(  1.0f, -1.0f,  0.0f );   // Bottom right
    glTexCoord2f( 1.0f, 1.0f );
    glVertex3f(  1.0f,  1.0f,  0.0f );   // Top right
    glTexCoord2f( 0.0f, 1.0f );
    glVertex3f( -1.0f,  1.0f,  0.0f );   // Top left
    glEnd();

    glBindTexture( GL_TEXTURE_2D, texture[ 1 ] );   // Select our texture

    glBegin( GL_QUADS );
    // side
    glTexCoord2f( 1.0f, 0.0f );
    glVertex3f(  0.0f, -1.0f, -1.0f );   // Bottom right
    glTexCoord2f( 1.0f, 1.0f );
    glVertex3f(  0.0f,  1.0f, -1.0f );   // Top right
    glTexCoord2f( 0.0f, 1.0f );
    glVertex3f(  0.0f,  1.0f,  1.0f );   // Top left
    glTexCoord2f( 0.0f, 0.0f );
    glVertex3f(  0.0f, -1.0f,  1.0f );   // Bottom left
    glEnd();


    glBindTexture( GL_TEXTURE_2D, texture[ 2 ] );   // Select our texture

    glBegin( GL_QUADS );
    // Top
    glTexCoord2f( 0.0f, 1.0f );
    glVertex3f( -1.0f,  0.0f, -1.0f );   // Top left
    glTexCoord2f( 0.0f, 0.0f );
    glVertex3f( -1.0f,  0.0f,  1.0f );   // Bottom left
    glTexCoord2f( 1.0f, 0.0f );
    glVertex3f(  1.0f,  0.0f,  1.0f );   // Bottom right
    glTexCoord2f( 1.0f, 1.0f );
    glVertex3f(  1.0f,  0.0f, -1.0f );   // Top right
    glEnd();

    glDisable(GL_TEXTURE_2D); 

 glColor3f (1.0, 1.0, 1.0); 
 glDisable(GL_CULL_FACE);
 glFrontFace(GL_CW);
 glutSolidTeapot(200.0);


[self postRemoteImage];

[[self openGLContext] flushBuffer];
}

Answer 1

Is this the entire code for the relevant methods? If so, you're never grabbing the mouse's position when you're dragging. curPos[] is uninitialized and may be returning the same values for each time you get a mouseDragged: message. This may make your object always rotate to the same position, making it appear like it's not moving.

Try inserting an NSLog in your mouseDragged: method to make sure that it's being called for your mouse drags (it probably is, but it's good to check).

There's a slight possibility that you're not giving the main run loop a chance to refresh the display, but I think that's unlikely. I've done something similar in my code and had it work just fine with everything on the main thread.

Rather than rolling your own trackball implementation, I suggest looking at Bill Dudney's trackball example code. While it is for the iPhone and deals with Core Animation, the trackball object he uses should be applicable to your case.