glReadPixels

[V--man]

The problem is the parameters you pass to glReadPixels.

Try

glReadPixels(1, 1, x, y, ...)

assuming x and y are higher than 1. I already answered this exact question in the gl ng. Are you that same person?

Besides, why not do
glReadPixels(0, 0, x, y, ....)

V-man

[Dagana]

I think my depth buffer is enable!?! glEnable(GL_DEPTH) does not exist. Only GL_DEPTH_TEST. If is what you're talking about I try it and nothing change, and I verify whit glIsEnable(...)! glReadPixels always return 1 in my Z variable.

Does anybody know how to calculate by myself the z of a mouse point?

Originally posted by Sebb:
I assure that I don't take you for a dummy but are you sure your depth buffer is enabled when you are drawing your scene ? (glEnable(GL_DEPTH)) And Are you sure your clear it at the beginning of each new frame ?

[Dagana]

No I am not the same person! I try this but my program crash.. :0 But the parameter of the glReadPixels is not glReadPixels(mouse.x, mouse.y, width of a pixels, height of a pixels, format, type, return value)??

If I do what you tell me, I'm not doing a big rectangle starting at the bottom, left corner? I have a picture made of points and I want the user to be able to draw a rectangle with the mouse, I translate this window coordinate in glCoordinate and take all the points inside of this region for finally made a croping of my picture.

Originally posted by V--man:
The problem is the parameters you pass to glReadPixels.

Try

glReadPixels(1, 1, x, y, ...)

assuming x and y are higher than 1. I already answered this exact question in the gl ng. Are you that same person?

Besides, why not do
glReadPixels(0, 0, x, y, ....)

V-man

[zed]

glClear ( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

glEnable( GL_DEPTH_TEST );
glDepthMask( GL_TRUE );
glBegin( GL_POINTS );
glVertex3f( 10,10,0 );
glEnd();

GLfloat z;
glReadPixels( 10, 10, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &z);
printf("%f\n", z );

gives me about 0.499 using glOrtho( 0, window_Width, 0 , window_Height, -1.0, 1.0 );