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.TH "ALLEGRO_PRIM_ATTR" "3alleg5" "" "Allegro reference manual" ""
.hy
.SH NAME
.PP
ALLEGRO_PRIM_ATTR - Allegro 5 API
.SH SYNOPSIS
.IP
.nf
\f[C]
#include <allegro5/allegro_primitives.h>

typedef enum ALLEGRO_PRIM_ATTR
\f[R]
.fi
.SH DESCRIPTION
.PP
Enumerates the types of vertex attributes that a custom vertex may have.
.IP \[bu] 2
ALLEGRO_PRIM_POSITION - Position information, can be stored only in
ALLEGRO_PRIM_SHORT_2, ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_FLOAT_3.
.IP \[bu] 2
ALLEGRO_PRIM_COLOR_ATTR - Color information, stored in an
ALLEGRO_COLOR(3alleg5).
The storage field of ALLEGRO_VERTEX_ELEMENT is ignored
.IP \[bu] 2
ALLEGRO_PRIM_TEX_COORD - Texture coordinate information, can be stored
only in ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_SHORT_2.
These coordinates are normalized by the width and height of the texture,
meaning that the bottom-right corner has texture coordinates of (1, 1).
.IP \[bu] 2
ALLEGRO_PRIM_TEX_COORD_PIXEL - Texture coordinate information, can be
stored only in ALLEGRO_PRIM_FLOAT_2 and ALLEGRO_PRIM_SHORT_2.
These coordinates are measured in pixels.
.IP \[bu] 2
ALLEGRO_PRIM_USER_ATTR - A user specified attribute.
You can use any storage for this attribute.
You may have at most ALLEGRO_PRIM_MAX_USER_ATTR (currently 10) of these
that you can specify by adding an index to the value of
ALLEGRO_PRIM_USER_ATTR, e.g.\ the first user attribute is
\f[C]ALLEGRO_PRIM_USER_ATTR + 0\f[R], the second is
\f[C]ALLEGRO_PRIM_USER_ATTR + 1\f[R] and so on.
.RS 2
.PP
To access these custom attributes from GLSL shaders you need to declare
attributes that follow this nomenclature: \f[C]al_user_attr_#\f[R] where
# is the index of the attribute.
.PP
For example to have a position and a normal vector for each vertex you
could declare it like this:
.IP
.nf
\f[C]
ALLEGRO_VERTEX_ELEMENT elements[3] = {
    {ALLEGRO_PRIM_POSITION, ALLEGRO_PRIM_FLOAT_3, 0},
    {ALLEGRO_PRIM_USER_ATTR + 0, ALLEGRO_PRIM_FLOAT_3, 12},
    {0, 0, 0}};
\f[R]
.fi
.PP
And then in your vertex shader access it like this:
.IP
.nf
\f[C]
attribute vec3 al_pos; // ALLEGRO_PRIM_POSITION
attribute vec3 al_user_attr_0; // ALLEGRO_PRIM_USER_ATTR + 0
varying float light;
const vec3 light_direction = vec3(0, 0, 1);
void main() {
    light = dot(al_user_attr_0, light_direction);
    gl_Position = al_pos;
}
\f[R]
.fi
.PP
To access these custom attributes from HLSL you need to declare a
parameter with the following semantics: \f[C]TEXCOORD{# + 2}\f[R] where
# is the index of the attribute.
E.g.
the first attribute can be accessed via \f[C]TEXCOORD2\f[R], second via
\f[C]TEXCOORD3\f[R] and so on.
.PP
Since: 5.1.6
.RE
.SH SEE ALSO
.PP
ALLEGRO_VERTEX_DECL(3alleg5), ALLEGRO_PRIM_STORAGE(3alleg5),
al_attach_shader_source(3alleg5)