Porting Polygons and Quadrilaterals

Keep the following points in mind when porting polygons and quadrilaterals:

• There is no direct equivalent for concave(TRUE). Instead you can use the tessellation routines in the GLU, described in Tessellating Polygons.
• Polygon modes are set differently.
• These polygon drawing functions have no direct equivalents in OpenGL: the poly family of routines; the polf family of routines; pmv, pdr, and pclos; rpmv and rpdr; splf; and spclos.

If your IRIS GL code uses these functions, you'll have to rewrite the code using glBegin(GL_POLYGON).

The following table lists the IRIS GL polygon drawing functions and their equivalent OpenGL functions.

Porting Polygon Modes

The OpenGL function glPolygonMode lets you specify which side of a polygon (the back or the front) the mode applies to. Its syntax is:

void glPolygonMode( GLenum face, GLenum mode ); 
 

where face is one of:

The GL_FRONT_AND_BACK mode is equivalent to the IRIS GL polymode function. The following table lists IRIS GL polygon modes and their equivalent OpenGL modes.

Porting Polygon Stipples

When porting IRIS GL polygon stipples, keep the following points in mind:

• OpenGL doesn't use tables for polygon stipples; only one stipple pattern is kept. You can use display lists to store different stipple patterns.
• The OpenGL polygon stipple bitmap size is always a 32x32 bit pattern.
• Stipple encoding is affected by glPixelStore.

For more information on porting polygon stipples, see Porting Pixel Operations.

The following table lists IRIS GL polygon stipple functions and their equivalent OpenGL functions.

In OpenGL, you enable and disable polygon stippling by passing GL_POLYGON_STIPPLE as a parameter for glEnable and glDisable.

The following OpenGL code sample demonstrates polygon stippling:

void display(void) 
{ 
    GLubyte fly[] = { 
      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
      0x03, 0x80, 0x01, 0xC0, 0x06, 0xC0, 0x03, 0x60, 
      0x04, 0x60, 0x06, 0x20, 0x04, 0x30, 0x0C, 0x20, 
      0x04, 0x18, 0x18, 0x20, 0x04, 0x0C, 0x30, 0x20, 
      0x04, 0x06, 0x60, 0x20, 0x44, 0x03, 0xC0, 0x22, 
      0x44, 0x01, 0x80, 0x22, 0x44, 0x01, 0x80, 0x22, 
      0x44, 0x01, 0x80, 0x22, 0x44, 0x01, 0x80, 0x22, 
      0x44, 0x01, 0x80, 0x22, 0x44, 0x01, 0x80, 0x22, 
      0x66, 0x01, 0x80, 0x66, 0x33, 0x01, 0x80, 0xCC, 
      0x19, 0x81, 0x81, 0x98, 0x0C, 0xC1, 0x83, 0x30, 
      0x07, 0xe1, 0x87, 0xe0, 0x03, 0x3f, 0xfc, 0xc0, 
      0x03, 0x31, 0x8c, 0xc0, 0x03, 0x33, 0xcc, 0xc0, 
      0x06, 0x64, 0x26, 0x60, 0x0c, 0xcc, 0x33, 0x30, 
      0x18, 0xcc, 0x33, 0x18, 0x10, 0xc4, 0x23, 0x08, 
      0x10, 0x63, 0xC6, 0x08, 0x10, 0x30, 0x0c, 0x08, 
      0x10, 0x18, 0x18, 0x08, 0x10, 0x00, 0x00, 0x08 
    }; 
    GLubyte halftone[] = { 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55, 
      0xAA, 0xAA, 0xAA, 0xAA, 0x55, 0x55, 0x55, 0x55 
    }; 
 
    glClear (GL_COLOR_BUFFER_BIT); 
 
/*  draw all polygons in white*/ 
    glColor3f (1.0, 1.0, 1.0); 
 
/*  draw one solid, unstippled rectangle,*/ 
/*  then two stippled rectangles*/ 
    glRectf (25.0, 25.0, 125.0, 125.0); 
    glEnable (GL_POLYGON_STIPPLE); 
    glPolygonStipple (fly); 
    glRectf (125.0, 25.0, 225.0, 125.0); 
    glPolygonStipple (halftone); 
    glRectf (225.0, 25.0, 325.0, 125.0); 
    glDisable (GL_POLYGON_STIPPLE); 
 
    glFlush (); 
} 
 

Porting Tessellated Polygons

In IRIS GL, you use concave(TRUE) and then bgnpolygon to draw concave polygons. The OpenGL GLU includes functions you can use to draw concave polygons.

    To draw a concave polygon with OpenGL

1. Create a tessellation object.
2. Define callbacks that will be used to process the triangles generated by the tessellator.
3. Specify the concave polygon to be tessellated.

The following table lists the OpenGL functions for drawing tessellated polygons.