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OpenGL 2D Examples - 102 Using the Basics

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Baker Joined: 14 Mar 2006 Posts: 1538 |

Posted: Wed Dec 17, 2008 3:03 am Post subject: OpenGL 2D Examples - 102 Using the Basics |

This focuses on applying the 2D basics and assumes you understand: 1. how draw a line/point/polygon 2. anti-alias them if needed 3. Know the basic opengl functions All this was covered in the last thread which ended with drawing a speedometer needle on a speedometer texture:
This thread is going to start to get into applying these concepts to try things and then getting into alpha masking and alpha blending and more versatile use of textures.
Drawing a Checkboard
Not much explanation is needed here, but the reason I am bothering to do this is because one common use of 2D graphics is tile oriented games.
Initialization:

Code:
glClearColor (0, 0, 0, 0) glMatrixMode (GL_PROJECTION) // Projection matrix glOrtho(0, 512, 512, 0, 0, 1) // Define 2D coordinates = 512 x 512

Rendering each frame:

Code:
glClear (GL_COLOR_BUFFER_BIT) // Clear it For i = 0 To 7 For j = 0 To 7 If (i + j) And 1 Then // Even=odd test glColor3f (1, 1, 1) // White
Else
glColor3f (1, 0, 0) // Red
End If
glBegin (GL_QUADS)
x1 = i * 32 + 128 // 128 = left start, 32 = tile size
y1 = j * 32 + 128 // 128 = top start, 32 = tile size
x2 = x1 + 32
y2 = y1 + 32
glVertex2d (x1, y1)
glVertex2d (x2, y1)
glVertex2d (x2, y2)
glVertex2d (x1, y2)
glEnd ()
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