An overlay image

OpenGL OpenGL: Basic Coding
1

Say I have a spinning cube like so:

How do I add a 2d image in the forground like so:

2

Disable depth test, set up an ortho projection and draw your image.

3

Erm, could you give me the code to see (I am very new to this, sorry).

4

this set ortho projection


/**
 * @brief Sets the orthographic projection to draw 2D objects. Here it is used to display texts on the screen.
 * Note that origin is the upper left corner and coordinates unit is the pixel. w= screen width, h= screen height
 */
void setOrthographicProjection()
{
	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();
	// set a 2D orthographic projection
	gluOrtho2D(0, w, 0, h);
	// invert the y axis, down is positive
	glScalef(1, -1, 1);
	// mover the origin from the bottom left corner
	// to the upper left corner
	glTranslatef(0, -h, 0);
	glMatrixMode(GL_MODELVIEW);
}

taken from lighthouse3D glut tutorial.

5

Some pseudocode:


# width and height are width and height of the window
glMatrixMode(GL_PROJECTION)
glPushMatrix # save the current projection matrix
glLoadIdentity
gluOrtho(0, width, 0, height)

# now one GL unit corresponds to one window pixel, so you can position your image
# draw image

glPopMatrix # restore old matrix
6

Okay, thank you this works at first but as i change gluLookAt it looks at the picture in the over from a different angle as well, and how would i go about stopping gluLookAt from applying to this one image?

7

You are right… you also have to “deactivate” the modelview matrix; simply load it to be the identity matrix. You’ll figure it out :wink:

8

No, I am really not that good. I tried putting
glMatrixMode(GL_PROJECTION);
before i drew the image and then
glMatrixMode(GL_MODELVIEW);
afterwards, but that had no effect

9

Sorted Now!!