GLUT bitmap fonts have unexpected position

Question

I am making a game in OpenGL using GLUT on UNIX. It is a 3D game where the player can move side to side (x-axis) jump (y-axis) and is constantly moving forward and has to avoid oncoming obstacles (for my implementation the player actual stands still while the world constantly moves at the player).

I am having trouble when trying to draw a HUD with bitmap text on it. I have tried creating an orthogonal view and then drawing the text but it always ends up at a random spot on the x-axis and constantly moves towards the player with the world on the z-axis. Once it gets past the player it disappears (which is what happens to all the world objects to cut processing). I want the text in one place and to stay there.

gameSpeed = Accumulator*6;

DrawRobot(); //player

ModelTrans.loadIdentity(); //ModelTrans has helper functions to manipulate
ModelTrans.pushMatrix();   //the current matrix stack
ModelTrans.translate(vec3(0, 0, -gameSpeed)); //move the whole world

...Then I do a bunch of drawing of the game objects...

And here I attempt to do some bitmap fonts. Disabling the depth test helps put the text in front of all the other objects but the other code to create the orthogonal view actually could be commented out and I would still have the same problem.

ModelTrans.popMatrix();

glDisable(GL_DEPTH_TEST);
glMatrixMode(GL_PROJECTION);
ModelTrans.pushMatrix();
glLoadIdentity();
gluOrtho2D(0, WindowWidth, 0, WindowHeight);
glScalef(1, -1, 1);
glTranslatef(0, -WindowHeight, 0);
glMatrixMode(GL_MODELVIEW);

std::string str = "sup";
renderBitmapString(0.5 + xText, 5.0, GLUT_BITMAP_HELVETICA_18, str);
//xText adjusts for the moving left and right of the player

glMatrixMode(GL_PROJECTION);
ModelTrans.popMatrix();
glMatrixMode(GL_MODELVIEW);

glUseProgram(0);
glutSwapBuffers();
glutPostRedisplay();
printOpenGLError();

Here is some other code that may be of use:

void renderBitmapString(float x, float y, void *font, std::string s)
{
   glRasterPos2f(x, y);

   for (string::iterator i = s.begin(); i != s.end(); ++i)
   {
      char c = *i;
      glutBitmapCharacter(font, c);
   }
}

void Timer(int param)
{
    Accumulator += StepSize * 0.001f;
    glutTimerFunc(StepSize, Timer, 1);
}

void Reshape(int width, int height)
{
    WindowWidth = width;
    WindowHeight = height;
    glViewport(0, 0, width, height);
}

score 0 · Answer 1 · answered Jun 11 '13 at 09:51

I am making a game in OpenGL using GLUT on UNIX

First of all, you're not doing it on Unix, but most likely using X11. Also I'm pretty sure your OS is a variant of Linux, which is not Unix (a …BSD would be a true Unix).

Anyway, in this code snippet you're adjusting the projection, but not the modelview matrix

glMatrixMode(GL_PROJECTION);
ModelTrans.pushMatrix();
glLoadIdentity();
gluOrtho2D(0, WindowWidth, 0, WindowHeight);
glScalef(1, -1, 1);
glTranslatef(0, -WindowHeight, 0);
glMatrixMode(GL_MODELVIEW);

std::string str = "sup";
renderBitmapString(0.5 + xText, 5.0, GLUT_BITMAP_HELVETICA_18, str);
//xText adjusts for the moving left and right of the player

glMatrixMode(GL_PROJECTION);
ModelTrans.popMatrix();
glMatrixMode(GL_MODELVIEW);

I'm not entirely sure what ModelTrans is, but it has pushMatrix and popMatrix and if I assume, that those are just glPushMatrix and glPopMatrix then your code mises a

glPushMatrix();
glLoadIdentity()

…

glPopMatrix();

block acting on the Modelview matrix. Modelview and Projection matrices have their own stacks in OpenGL and must be pushed/poped individually.

GLUT bitmap fonts have unexpected position

1 Answers1