OpenGL Basic Drawing

With the exception of glRect(), most drawing is done by creating geometric objects using glBegin()...glEnd() combination, where between each such pair you specify a collection of vertices that define the object. Along with specifying vertices, you can specify a number of attributes that affect how the vertices will appear. These include things such as color, surface normals (for shading), and texture coordinates (for texture mapping).

glRect*(...):

Draw a rectangle on the z=0 plane. The arguments give the (x,y) coordinates of any two opposite corners of the rectangle. Some forms include glRectd(), which takes four double's, glRectf(), which takes four float's, glRectfv() takes two vectors, each consisting of two float's.

glBegin(GLenum mode)...glEnd(void):

Define an object, where mode may be any of:

• GL_POINTS: set of points
• GL_LINES: set of line segments (not connected)
• GL_LINE_STRIP: chain of connected line segments
• GL_LINE_LOOP: closed polygon (may self intersect)
• GL_TRIANGLES: set of triangles (not connected)
• GL_TRIANGLE_STRIP: linear chain of triangles
• GL_TRIANGLE_FAN: fan of triangles (joined to one point)
• GL_QUADS: set of quadrangles (not connected)
• GL_QUAD_STRIP: linear chain of quadrangles
• GL_POLYGON: a convex polygon

There is a limited set of commands that can be placed within glBegin()..glEnd() pairs. These include glVertex*(), glColor*(), glNormal*(), glTexCoord*(), glMaterial*(), and glCallList(). See the reference manual for the exact specification of vertex order and orientation.

glVertex*(...):

Specify the coordinates of a vertex.

glNormal*(...):

Specify the surface normal for subsequent vertices. The normal should be of unit length after the modelview transformation is applied. Call glEnable(GL_NORMALIZE) to have OpenGL do normalization automatically.

glColor*(...):

Specify the color of subsequent vertices. This is normally used if lighting is not enabled. Otherwise, colors are defined by glMaterial*(), defined below under lighting.

glLineWidth(GLfloat width):

Sets the line width for subsequent line drawing. The argument is the width of the line (in pixels). (Note that not all widths are necessarily supported.)

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Last updated: Sat, Feb 8, 2003.