🚀 go-pugleaf

In article <7671@dove.nist.gov>, fred@poly2.nist.gov writes:
> Suppose you have a material color:
> 
> float object_color[] = 
> {
>         DIFFUSE,    0.1, 1.0, 0.2,
>         SPECULAR,   0.3, 0.9, 0.3,
>         EMISSION,   1.0, 0.1, 1.0,
>         SHININESS,  24.0,
>         LMNULL 
> };
> 
> which has been set with:
> 
> 	lmdef(DEFMATERIAL, 1, 15, object_color);
> 
> 
> First, are you allowed to change the EMISSION values (or really any
> of object_color's properties) on the fly?  

Yes.

> 
> Second, If you can change on the fly, do you need to do a new call to
> lmdef every time for the changes to take effect or is the first call
> sufficient?
> 

You have to call lmdef each time:

float object_color[] = 

{
	DIFFUSE,    0.1, 1.0, 0.2,
	SPECULAR,   0.3, 0.9, 0.3,
	EMISSION,   1.0, 0.1, 1.0,
	SHININESS,  24.0,
	LMNULL 
};

float object_color_emission[] = {
	EMISSION,   1.0, 0.1, 1.0,
	LMNULL
};

	

	lmdef(DEFMATERIAL,1,0,object_color);
	lmbind(MATERIAL,1);
	draw_stuff();
	object_color_emission[2] = .2;

	/*
	 * Since material #1 is bound, these changes will take place now.
	 * Only emission is changed.
	 */
	lmdef(DEFMATERIAL,1,0,object_color_emission);
	
	draw_stuff();

If you have LOTS of such changes, uou can use lmcolor:

	float c[][3] = {
		0,0,0,
		.1,0,0,
		0.,.1,0,	etc.
	};

	lmdef(DEFMATERIAL,1,0,object_color);
	lmbind(MATERIAL,1);
	lmcolor(LMC_EMISSION);

	/* new emission for each polygon ... */
	for( i = 0; i < sizeof(c)/sizeof(c[0]); i++) {
		c3f(c[i]);
		draw_polygon(i);
	}

	/* new emission for each vertex ... */
	bgnpolygon();
	for( i = 0; ...; i++) {
		c3f(c[i]);
		n3f(n[i]);
		v3f(v[i]);
	}
	endpolygon();


	LMC_AD is a popular way to use lmcolor.



	


Reuel Nash	(713)293-9292	FAX (713)293-0503
Silicon Graphics, 11490 Westheimer Suite 100, Houston, TX  77077

Visualize Whirled Peas

In <7671@dove.nist.gov> fred@poly2.nist.gov (Frederick R. Phelan Jr.) writes:
>Suppose you have a material color:
>float object_color[] = 
>{
>        DIFFUSE,    0.1, 1.0, 0.2,
>        SPECULAR,   0.3, 0.9, 0.3,
>        EMISSION,   1.0, 0.1, 1.0,
>        SHININESS,  24.0,
>        LMNULL 
>};
>which has been set with:
>	lmdef(DEFMATERIAL, 1, 15, object_color);
>First, are you allowed to change the EMISSION values (or really any
>of object_color's properties) on the fly?  

Yes.  Use lmcolor(LMC_EMISSION) if you are only changing that one
property, and use c3f() or cpack() commands to change it.

>Second, If you can change on the fly, do you need to do a new call to
>lmdef every time for the changes to take effect or is the first call
>sufficient?

Changing the value in the array is not sufficient-- you need to send
the values to the GL.  Use lmcolor() if you can, or just issue another
lmdef() with just the values you are changing:

float object_emission[] = { EMISSION, 0.2, 0.5, 0.1, LMNULL };
lmdef(DEFMATERIAL, 1, 5, object_emission);

In OpenGL, this is much simpler-- material properties are just like
colors.  You set them and forget them.

So, in OpenGL, your code will look like:

float emission[3] = { 1.0, 0.1, 1.0 };
glMaterialfv(GL_FRONT, GL_EMISSION, emission);

... no bind necessary.
--
--gavin     (gavin@sgi.com,  (415)390-1024)