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build_shader(3) 		  Arcan Lua API 		 build_shader(3)

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  de-
     fined.  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 ver-
     tex_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), bi-
	    tangent (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),  time-
	    stamp (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)

vidsys				   August 2026			 build_shader(3)

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