NAME

build_shader - using

SYNOPSIS

uint:shader_id
build_shader( string/nil:vertex_program, string/nil:fragment_program, string:label )

DESCRIPTION

All video objects can have a series of processing/ rendering instructions associated with them. These are platform dependent, and you can check ( GL_VERSION , SHADER_LANGUAGE ) for identification strings to help support your choice, and the most commonly supported shader language is currently GLSL 120. This function is used to go from a higher level description (like a string) to some implementation defined internal interpretation that can later be referenced and connected to VID s using the returned shader_id or the label . vertex_program describes the processing stage that determines the shape of the object to be drawn, and fragment_program the content that will be filled inside the shape. Both of these are allowed to be nil, and the engine will then use whatever platform specific default that is defined. A shader can also have a set of limited user-defined variables, called _uniforms_ (see shader_uniform for details) along with a number of built in ones (see the notes below). If the contents of the supplied vertex_program or fragment_program could not be interpreted, or there was insufficient shader slots left to create another one, the returned shader_id will be nil. To associate a successfully built shader to a vid, see image_shader .

NOTES

1

For GLSL 120, reserved attributes are: vertex (vec4), normal (vec3), color (vec4), texcoord (vec2), texcoord1 (vec2), tangent (vec3), bitangent (vec3), joints (ivec4), weights (vec4)

2

For GLSL 120, reserved uniforms are: modelview (mat4), projection (mat4), texturem (mat4), trans_move (float, 0.0 .. 1.0), trans_scale (float, 0.0 .. 1.0) trans_rotate (float, 0.0 .. 1.0), obj_input_sz (vec2, orig w/h) obj_output_sz (vec2, current w/h), obj_storage_sz (vec2, texture storage w/h), obj_opacity(float, 0.0 .. 1.0), obj_col (vec3, 0.0 .. 1.0), rtgt_id (uint), fract_timestamp (float), timestamp (int)

EXAMPLE

local shfmt = {};
shfmt["GLSL120"].vertex = [[
uniform mat4 modelview;
uniform mat4 projection;
attribute vec4 vertex;
attribute vec2 texcoord;
varying vec2 texco;
void build_shader0(void)
{


      texco = texcoord;


      gl_Position = (projection * modelview) * vertex;
}
]];
shfmt["GLSL120"].fragment = [[
uniform sampler2D map_diffuse;
uniform float obj_opacity;
varying vec2 texco;
void build_shader0(){


            vec4 col = texture2D(map_diffuse, texco);


            col.a = col.a * obj_opacity;


            gl_FragColor = col;
}
]];
function build_shader0()


      local sh = shfmt[SHADER_LANGUAGE];


      if (sh == nil) then


            return shutdown("no matching shader for the platform language:" ..


                  SHADER_LANGUAGE, EXIT_FAILURE);


      end


      build_shader(sh.vertex, sh.fragment, "default");
end

MISUSE

local shfmt = {};
shfmt["GLSL120"].vertex = [[
uniform mat4 modelview;
uniform mat4 projection;
attribute vec4 vertex;
attribute vec2 texcoord;
varying vec2 texco;
void build_shader0(void)
{


      texco = texcoord;


      gl_Position = (projection * modelview) * vertex;
}
]];
shfmt["GLSL120"].fragment = [[
uniform sampler2D map_diffuse;
uniform float obj_opacity;
varying vec2 texco;
void build_shader0(){


            vec4 col = texture2D(map_diffuse, texco);


            col.a = col.a * obj_opacity;


            gl_FragColor = col;
}
]];
function build_shader0()


      local sh = shfmt[SHADER_LANGUAGE];


      if (sh == nil) then


            return shutdown("no matching shader for the platform language:" ..


                  SHADER_LANGUAGE, EXIT_FAILURE);


      end


      build_shader(nil, nil, nil);
end

MISUSE

local shfmt = {};
shfmt["GLSL120"].vertex = [[
uniform mat4 modelview;
uniform mat4 projection;
attribute vec4 vertex;
attribute vec2 texcoord;
varying vec2 texco;
void build_shader1(void)
{


      texco = texcoord;


      gl_Position = (projection * modelview) * vertex;
}
]];
shfmt["GLSL120"].fragment = [[
uniform sampler2D map_diffuse;
uniform float obj_opacity;
varying vec2 texco;
void build_shader1(){


            vec4 col = texture2D(map_diffuse, texco);


            col.a = col.a * obj_opacity;


            gl_FragColor = col;
}
]];
function build_shader1()


      local sh = shfmt[SHADER_LANGUAGE];


      if (sh == nil) then


            return shutdown("no matching shader for the platform language:" ..


                  SHADER_LANGUAGE, EXIT_FAILURE);


      end


      build_shader(vshader, fshader, 0.5);
end

SEE ALSO:

shader_uniform(3) image_shader(3) shader_ugroup(3) delete_shader(3)