ALLEGRO_PRIM_ATTR(3)

1ALLEGRO_PRIM_ATTR(3)                                      ALLEGRO_PRIM_ATTR(3)
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NAME

6       ALLEGRO_PRIM_ATTR - Allegro 5 API
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SYNOPSIS

9              #include <allegro5/allegro_primitives.h>
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11              typedef enum ALLEGRO_PRIM_ATTR
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DESCRIPTION

14       Enumerates  the  types  of  vertex  attributes that a custom vertex may
15       have.
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17       • ALLEGRO_PRIM_POSITION - Position information, can be stored  only  in
18         ALLEGRO_PRIM_SHORT_2, ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_FLOAT_3.
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20       • ALLEGRO_PRIM_COLOR_ATTR  -  Color  information,  stored  in  an ALLE‐
21         GRO_COLOR(3).  The storage field of ALLEGRO_VERTEX_ELEMENT is ignored
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23       • ALLEGRO_PRIM_TEX_COORD  -  Texture  coordinate  information,  can  be
24         stored  only in ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_SHORT_2.  These
25         coordinates are normalized by the width and height  of  the  texture,
26         meaning  that  the bottom-right corner has texture coordinates of (1,
27         1).
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29       • ALLEGRO_PRIM_TEX_COORD_PIXEL - Texture coordinate information, can be
30         stored  only in ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_SHORT_2.  These
31         coordinates are measured in pixels.
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33       • ALLEGRO_PRIM_USER_ATTR - A user specified attribute.  You can use any
34         storage   for   this   attribute.    You   may  have  at  most  ALLE‐
35         GRO_PRIM_MAX_USER_ATTR (currently 10) of these that you  can  specify
36         by  adding  an index to the value of ALLEGRO_PRIM_USER_ATTR, e.g. the
37         first user attribute is ALLEGRO_PRIM_USER_ATTR + 0, the second is AL‐
38         LEGRO_PRIM_USER_ATTR + 1 and so on.
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40         To  access  these custom attributes from GLSL shaders you need to de‐
41         clare attributes that follow this nomenclature: al_user_attr_#  where
42         # is the index of the attribute.
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44         For  example  to  have a position and a normal vector for each vertex
45         you could declare it like this:
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47                ALLEGRO_VERTEX_ELEMENT elements[3] = {
48                    {ALLEGRO_PRIM_POSITION, ALLEGRO_PRIM_FLOAT_3, 0},
49                    {ALLEGRO_PRIM_USER_ATTR + 0, ALLEGRO_PRIM_FLOAT_3, 12},
50                    {0, 0, 0}};
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52         And then in your vertex shader access it like this:
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54                attribute vec3 al_pos; // ALLEGRO_PRIM_POSITION
55                attribute vec3 al_user_attr_0; // ALLEGRO_PRIM_USER_ATTR + 0
56                varying float light;
57                const vec3 light_direction = vec3(0, 0, 1);
58                void main() {
59                    light = dot(al_user_attr_0, light_direction);
60                    gl_Position = al_pos;
61                }
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63         To access these custom attributes from HLSL you need to declare a pa‐
64         rameter  with the following semantics: TEXCOORD{# + 2} where # is the
65         index of the attribute.  E.g.  the first attribute  can  be  accessed
66         via TEXCOORD2, second via TEXCOORD3 and so on.
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68         Since: 5.1.6
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NAME

SYNOPSIS

DESCRIPTION

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