Drawing a simple rectangle as raster font background

OpenGL OpenGL: Basic Coding
1

Hello!

I would like to draw a simple rectangle, say 200 x 50 pixels (as background to a raster font generated with wglUseFontBitmaps).

Is there a smarter way to do it than to use glBitmap and a gigantic array of one:s?

(I guess using glBegin(GL_QUADS) or something similar won’t work for me as I want to specify the size of this rectangle in pixels, whereas GL_QUADS wants me to specify all vertexes of the rectangle).

// David

2

if you use glOrtho(0, window_width, 0, window_height, -1., 1.), all values that you pass to glVertex() will be pixel units.

3

Thanks for your help, but the position of the rectangle should be somewhere in the scene (and affected by rotations etc), so I can’t use glOrtho to change the projection matrix.

The effect is somewhat like a speech bubble or an explanatory text related to an object.

// David

4

You can convert the 3D object space coordinates to 2D screencoordinates with gluProject:

// Coordinates in 2D:
GLdouble winX, winY, winZ;
// Project object coord to window coordinate
if (gluProject(x, y, z, modelMatrix, projMatrix, viewport, &winX, &winY, &winZ))
MyDrawStringFunction(s, winX, winY, winZ, txtCol, bckCol);