Introduction to AutoQ3D and OpenGL® API
AutoQ3D was born to design 3D models
taking advantage of OpenGL® API libraries to construct all the graphics
stuff. The main objective in mind is to offer a solution to create 3D
models with a very intuitive and easy to do things.
OpenGL® API is
an application programming interface which allow programmers take
advantage of 3D acceleration of video cards and display images;
basically it consists of a library of objects and 3D functions. It
provides default geometrical figures or shapes called primitives. More
complex figures are built up by combining this primitives.
AutoQ3D uses points primitives (GL_POINTS), lines primitives (GL_LINES) and triangles primitives (GL_TRIANGLES).
 OpenGL - Basic Geometrical Shapes - Primitives
Concepts to draw objects using OpenGL® API libraries
To draw objects using OpenGL® API libraries the points you use suffer a transformation to display them on the screen.
 Transformation process to display OpenGL primitives
As you see at the figure above, you first specify objects coordinates,
then you multiply by the ModelView Matrix where you apply the rotate
and transfering functions of the point in the space, then you multiply
by the proyection matrix which it adjusts to scale and perspective
parameters, then you do a perspective division and another
transformation to adjust to the window and finally locate the pixel
position on the screen.
Each pixel on the screen has information about
1. RGBA color
2. Depth (called Z-Buffer)
3. Stencil Buffer
"RGB"
channel corresponds to the pixel color and the "A" channel corresponds
to the value which you do the source pixel operation and target pixel
operation, frequently used for transparency effects.
"Z-Buffer" is used to make depth comparison and to draw or not the pixel, so hiding the objects.
To draw lines you must use parameters like:
1. Position Points
2. Object Color
To draw triangles, besides the above mentioned parameters you use parameters like:
1. Normals
2. Texture coordinates of each vertex
Normals
indicates the way the light interacts with the vertex illuminating
itself when ponits directly to light. When the normal of two triangles
match we can see the effect show on figure below.
 Texture position values
Textures can
be loaded from several graphical file formats as JPG, BMP, PNG. You
apply the texture coordinate to each vertex. Texture position value is
shown on the figure above.
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