NAME

       polygon3d, polygon3d_f - Draws a 3d polygon onto the specified bitmap. Allegro game programming library.

SYNOPSIS

       #include <allegro.h>

       void polygon3d(BITMAP *bmp, int type, BITMAP *texture, int vc, V3D *vtx[]);

       void polygon3d_f(BITMAP *bmp, int type, BITMAP *texture, int vc, V3D_f *vtx[]);

DESCRIPTION

       Draw  3d  polygons  onto  the  specified  bitmap,  using the specified rendering mode. Unlike the regular
       polygon() function, these routines don't support concave or self-intersecting shapes, and they can't draw
       onto  mode-X  screen  bitmaps (if you want to write 3d code in mode-X, draw onto a memory bitmap and then
       blit to the screen). The width and height of the texture bitmap  must  be  powers  of  two,  but  can  be
       different,  eg. a 64x16 texture is fine, but a 17x3 one is not. The vertex count parameter (vc) should be
       followed by an array containing the appropriate number of pointers to vertex structures: polygon3d() uses
       the  fixed  point  V3D structure, while polygon3d_f() uses the floating point V3D_f structure.  These are
       defined as:

          typedef struct V3D
          {
             fixed x, y, z;       - position
             fixed u, v;          - texture map coordinates
             int c;               - color
          } V3D;

          typedef struct V3D_f
          {
             float x, y, z;       - position
             float u, v;          - texture map coordinates
             int c;               - color
          } V3D_f;

       How the vertex data is used depends on the rendering mode:

       The `x' and `y' values specify the position of the vertex in 2d screen coordinates.

       The `z' value is only required when doing perspective correct texture mapping, and specifies the depth of
       the point in 3d world coordinates.

       The  `u'  and  `v'  coordinates  are only required when doing texture mapping, and specify a point on the
       texture plane to be mapped on to this vertex.  The texture plane is an infinite plane  with  the  texture
       bitmap  tiled  across it. Each vertex in the polygon has a corresponding vertex on the texture plane, and
       the image of the resulting polygon in the texture plane will be mapped on to the polygon on the screen.

       We refer to pixels in the texture plane as texels. Each texel is a block, not just  a  point,  and  whole
       numbers  for u and v refer to the top-left corner of a texel. This has a few implications. If you want to
       draw a rectangular polygon and map a texture sized 32x32 on to it, you would use the texture  coordinates
       (0,0),  (0,32),  (32,32)  and  (32,0),  assuming  the  vertices are specified in anticlockwise order. The
       texture will then be mapped perfectly on to the polygon. However, note that when we set  u=32,  the  last
       column  of  texels  seen  on  the screen is the one at u=31, and the same goes for v. This is because the
       coordinates refer to the top-left corner of the texels. In effect, texture coordinates at the  right  and
       bottom on the texture plane are exclusive.

       There is another interesting point here. If you have two polygons side by side sharing two vertices (like
       the two parts of folded piece of cardboard), and you want to map a texture across  them  seamlessly,  the
       values  of  u  and v on the vertices at the join will be the same for both polygons. For example, if they
       are both rectangular, one polygon may use (0,0), (0,32), (32,32)  and  (32,0),  and  the  other  may  use
       (32,0), (32,32), (64,32), (64,0). This would create a seamless join.

       Of  course you can specify fractional numbers for u and v to indicate a point part-way across a texel. In
       addition, since the texture plane is infinite, you can  specify  larger  values  than  the  size  of  the
       texture.  This can be used to tile the texture several times across the polygon.

       The `c' value specifies the vertex color, and is interpreted differently by various rendering modes. Read
       the beginning of chapter "Polygon rendering" for a  list  of  rendering  types  you  can  use  with  this
       function.

SEE ALSO

       triangle3d(3alleg4),   quad3d(3alleg4),   polygon(3alleg4),  clip3d(3alleg4),  cpu_capabilities(3alleg4),
       excamera(3alleg4)