Moving objects on screen by per pixel basis with glRasterPos()

c++, opengl, raster

Solution

Here's a small snippet of code that I use to render some debug text in a small application:

void
renderText(float x, float y, const char* text) {
    int viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    glOrtho(viewport[0], viewport[2], viewport[1], viewport[3], -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glRasterPos2f(x, viewport[3] - y);
    const int length = (int)strlen(text);
    for (int i = 0; i < length; ++i) {
        glutBitmapCharacter(GLUT_BITMAP_9_BY_15, text[i]);
    }
    glMatrixMode( GL_PROJECTION );
    glPopMatrix();
    glMatrixMode( GL_MODELVIEW );   
    glPopMatrix();
}

`x`and `y` is the desired window coordinates of the string. `glutBitmapCharacter(GLUT_BITMAP_9_BY_15, ...)` is just a utility function from GLUT that renders a 9 x 15 pixels large bitmap character.

Problem

I have the following code to render text in my app, first i get the mouse coordinates in the world, then use those coordinates to place my text in the world, so it will follow my mouse position: Edit: added buildfont() function in code example: ``` GLvoid BuildFont(GLvoid) // Build Our Bitmap Font { HFONT font; // Windows Font ID HFONT oldfont; // Used For Good House Keeping base = glGenLists(96); // Storage For 96 Characters font = CreateFont( -12, // Height Of Font 0, // Width Of Font 0, // Angle Of Escapement 0, // Orientation Angle FW_NORMAL, // Font Weight FALSE, // Italic FALSE, // Underline FALSE, // Strikeout ANSI_CHARSET, // Character Set Identifier OUT_TT_PRECIS, // Output Precision CLIP_DEFAULT_PRECIS, // Clipping Precision ANTIALIASED_QUALITY, // Output Quality FF_DONTCARE|DEFAULT_PITCH, // Family And Pitch "Verdana"); // Font Name (if not found, its using some other font) oldfont = (HFONT)SelectObject(hDC, font); // Selects The Font We Want wglUseFontBitmaps(hDC, 32, 96, base); // Builds 96 Characters Starting At Character 32 SelectObject(hDC, oldfont); // Selects The Font We Want DeleteObject(font); // Delete The Font } GLvoid glPrint(const char *fmt, ...){ char text[256]; va_list ap; if (fmt == NULL) return; va_start(ap, fmt); vsprintf(text, fmt, ap); va_end(ap); glPushAttrib(GL_LIST_BIT); glListBase(base - 32); glCallLists(strlen(text), GL_UNSIGNED_BYTE, text); glPopAttrib(); } ... glPushMatrix(); glColor4f(0,0,0,1); // X-1 wont work because these are the world coordinates: glRasterPos2d(MousePosX-1, MousePosY); glPrint("TEST"); glColor4f(1,1,0,1); glRasterPos2d(MousePosX, MousePosY); glPrint("TEST"); glPopMatrix(); ``` But i want to render multiline texts, or texts with "borders" (like in above code i tried) or text with background (so i could distinguish them better from the background) So how i do this? I just need to know how i can move it in pixels, so i could precisely modify the position on my screen WITHOUT using 2d projection view on top of my 3d render projection... i just want to make it as simple as possible. I tried to draw a quad under the text, but of course it doesnt work since its still using the world coordinates... so when i rotate my camera the text doesnt move along the background of the text... i am afraid the only solution is to create another projection on top of the 3d projection...

Original source