1polygon3d(3) Allegro manual polygon3d(3)
2
6 polygon3d, polygon3d_f - Draws a 3d polygon onto the specified bitmap.
7 Allegro game programming library.
8
10 #include <allegro.h>
11 void polygon3d(BITMAP *bmp, int type, BITMAP *texture, int vc, V3D
14 *vtx[]);
15 void polygon3d_f(BITMAP *bmp, int type, BITMAP *texture, int vc, V3D_f
17 *vtx[]);
18
20 Draw 3d polygons onto the specified bitmap, using the specified render‐
21 ing mode. Unlike the regular polygon() function, these routines don't
22 support concave or self-intersecting shapes, and they can't draw onto
23 mode-X screen bitmaps (if you want to write 3d code in mode-X, draw
24 onto a memory bitmap and then blit to the screen). The width and height
25 of the texture bitmap must be powers of two, but can be different, eg.
26 a 64x16 texture is fine, but a 17x3 one is not. The vertex count param‐
27 eter (vc) should be followed by an array containing the appropriate
28 number of pointers to vertex structures: polygon3d() uses the fixed
29 point V3D structure, while polygon3d_f() uses the floating point V3D_f
30 structure. These are defined as:
31 typedef struct V3D
33 {
34 fixed x, y, z; - position
35 fixed u, v; - texture map coordinates
36 int c; - color
37 } V3D;
38 typedef struct V3D_f
40 {
41 float x, y, z; - position
42 float u, v; - texture map coordinates
43 int c; - color
44 } V3D_f;
45 How the vertex data is used depends on the rendering mode:
47 The `x' and `y' values specify the position of the vertex in 2d screen
49 coordinates.
50 The `z' value is only required when doing perspective correct texture
52 mapping, and specifies the depth of the point in 3d world coordinates.
53 The `u' and `v' coordinates are only required when doing texture map‐
55 ping, and specify a point on the texture plane to be mapped on to this
56 vertex. The texture plane is an infinite plane with the texture bitmap
57 tiled across it. Each vertex in the polygon has a corresponding vertex
58 on the texture plane, and the image of the resulting polygon in the
59 texture plane will be mapped on to the polygon on the screen.
60 We refer to pixels in the texture plane as texels. Each texel is a
62 block, not just a point, and whole numbers for u and v refer to the
63 top-left corner of a texel. This has a few implications. If you want to
64 draw a rectangular polygon and map a texture sized 32x32 on to it, you
65 would use the texture coordinates (0,0), (0,32), (32,32) and (32,0),
66 assuming the vertices are specified in anticlockwise order. The texture
67 will then be mapped perfectly on to the polygon. However, note that
68 when we set u=32, the last column of texels seen on the screen is the
69 one at u=31, and the same goes for v. This is because the coordinates
70 refer to the top-left corner of the texels. In effect, texture coordi‐
71 nates at the right and bottom on the texture plane are exclusive.
72 There is another interesting point here. If you have two polygons side
74 by side sharing two vertices (like the two parts of folded piece of
75 cardboard), and you want to map a texture across them seamlessly, the
76 values of u and v on the vertices at the join will be the same for both
77 polygons. For example, if they are both rectangular, one polygon may
78 use (0,0), (0,32), (32,32) and (32,0), and the other may use (32,0),
79 (32,32), (64,32), (64,0). This would create a seamless join.
80 Of course you can specify fractional numbers for u and v to indicate a
82 point part-way across a texel. In addition, since the texture plane is
83 infinite, you can specify larger values than the size of the texture.
84 This can be used to tile the texture several times across the polygon.
85 The `c' value specifies the vertex color, and is interpreted differ‐
87 ently by various rendering modes. Read the beginning of chapter "Poly‐
88 gon rendering" for a list of rendering types you can use with this
89 function.
90
93 triangle3d(3), quad3d(3), polygon(3), clip3d(3), cpu_capabilities(3),
94 excamera(3)
95Allegro version 4.2.3 polygon3d(3)