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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  instruc-
       tions  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 lan-
       guage is	currently GLSL 120. This function is used to go	from a	higher
       level description (like a string) to some implementation	defined	inter-
       nal  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  insuffi-
       cient  shader slots left	to create another one, the returned shader_id
       will be nil. To associate a successfully	built shader to	a vid, see im-
       age_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), projec-
	      tion (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_opac-
	      ity(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)

vidsys				  April	2025		       build_shader(3)

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