Simplest OpenGL program ever -- not working...

BlitzMax Forums/OpenGL Module/Simplest OpenGL program ever -- not working...

SofaKng

(Posted 2007) [#1]

I'm taking this code from GameDev.net so I don't understand why it's not working.

What should be happening is that OpenGL is initialized for 2D (orthographical projection) and a simple line is drawn. However, in this case the screen is being cleared properly (according to glClearColor) but my line is not being drawn.

Can somebody please, please help me?

Here is the code:

GLGraphics 320, 200

Enable2D()

glClearColor(0.0, 0.0, 0.0, 0.0)	

While Not KeyHit(KEY_ESCAPE)
  glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT);

  glBegin(GL_LINE); 
    glVertex2i(0, 0) ; 
    glVertex2i(1, 1);
  glEnd();

  Flip()
Wend

Function Enable2D()
  
  Local vPort : Int[4]
  glGetIntegerv(GL_VIEWPORT, vPort);

  glMatrixMode(GL_PROJECTION) ; 
  glPushMatrix() ; 
  glLoadIdentity() ; 

  glOrtho(0, vPort[2], 0, vPort[3], -1, 1);

  glMatrixMode(GL_MODELVIEW) ;
  glPushMatrix() ; 
  glLoadIdentity();		
End Function

Function Disable2D()
	glMatrixMode(GL_PROJECTION) ; 
	glPopMatrix() ;
	glMatrixMode(GL_MODELVIEW) ; 
	glPopMatrix();	
End Function

Odds On

(Posted 2007) [#2]

You're drawing a line that is 1 pixel across and 1 pixel up. Also, GL_LINE should be GL_LINES. Change:

glBegin(GL_LINE);
glVertex2i(0, 0) ;
glVertex2i(1, 1);
glEnd();

to

glBegin(GL_LINES);
glVertex2i(0, 0) ;
glVertex2i(100, 100);
glEnd();

and it should work.

SofaKng

(Posted 2007) [#3]

Oh, sorry... I was using (10, 10) to (100, 100) but then I thought maybe OpenGL was using 0..1 screen coordinates.

Anyways, I think the problem was that I needed to use GL_LINES instead of GL_LINE.

Crazy typos...

Thanks for the help!