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>Blender Documentation Volume I - User Guide: Last modified April 29 2004 S68</TH
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><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="section_materials_glass"
></A
>Solid and Hollow Glass</H1
><P
>&#13;		Glass and tranparent materials are generally tricky to render 
		because they exhibit <I
CLASS="emphasis"
>refraction</I
>; that is,
		the bending of light rays due to the different <I
CLASS="emphasis"
>optical 
		density</I
>, or <I
CLASS="emphasis"
>index of refraction</I
>
		of the various materials. Unfortunately, to fully account for 
		refraction a ray tracer is mandatory. Still, we
		can produce convincing results in Blender using EnvMaps and advanced 
		Texturing techniques.
	</P
><P
>&#13;		Consider a scene with some basic geometries, including
		a cube, a cone, a sphere, and a torus. As a first example we will 
		make the 
		sphere look like a solid ball of glass and, as a second example, 
		that same sphere will become a glass bubble.
	</P
><P
>&#13;		To create this effect, we need to make the light appear to bend as 
		it passes through the sphere, since we would expect objects behind the solid 
		glass sphere to appear heavily warped, as if through a very
		thick lens. On the other hand, the hollow glass sphere's center should 
		be almost transparent
		while the sides should deflect light.
	</P
><DIV
CLASS="section"
><H2
CLASS="section"
><A
NAME="section_materials_solid_glass"
></A
>Solid Glass</H2
><P
>&#13;			1. To begin, we set up an environment map for the sphere's 
			material just as we did for the ball in the previous section, with an empty 
			which locates the
			EnvMap's perspective at the center of the sphere. 
		</P
><P
>&#13;			2. To fake Refraction we'll tweak the output mapping with the 
			<TT
CLASS="literal"
>ofsZ</TT
>,
			<TT
CLASS="literal"
>sizeX</TT
>, <TT
CLASS="literal"
>sizeY</TT
>, 
			<TT
CLASS="literal"
>sizeZ</TT
>
			 and <TT
CLASS="literal"
>Col</TT
> sliders to
			warp the map in a way that creates the effect of refraction. 
			To do so, use the settings in <A
HREF="x4736.html#BSG.MAT.F.S68.801"
>Figure 56</A
>.
		</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.801"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass01.png"></P
></DIV
><P
><B
>Figure 56. Envmap settings to fake refraction.</B
></P
></DIV
><P
>&#13;			3. Select the <TT
CLASS="literal"
>Mir</TT
> RGB material sliders and 
			lower the
			<TT
CLASS="literal"
>R</TT
> and <TT
CLASS="literal"
>G</TT
> a bit to give 
			the texture a blue tint. (Our experience with the idiosyncrasies of Blender's 
			handling of
			mirror colors dictates this unintuitive approach when 
			combining
			environment-mapped reflections and refractions in a single
			material.)
		</P
><P
>&#13;			4. Turn the <TT
CLASS="literal"
>Ref</TT
> slider all the way down. 
			(<A
HREF="x4736.html#BSG.MAT.F.S68.802"
>Figure 57</A
>).
			You should now have produced a blue-tinted refraction of the 
			environment. 
		</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.802"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass02.png"></P
></DIV
><P
><B
>Figure 57. Material settings</B
></P
></DIV
><P
>&#13;		5. Shiny
		glass also needs a reflection map, so we'll place the 
		<TT
CLASS="literal"
>same</TT
> texture into
		another texture channel. Press the <TT
CLASS="literal"
>Add</TT
>, 
		<TT
CLASS="literal"
>Col</TT
>,
		and <TT
CLASS="literal"
>Emit</TT
> buttons, and use the 
		<TT
CLASS="literal"
>Refl</TT
> button for
		the coordinates. Make the material <TT
CLASS="literal"
>Color</TT
> 
		black and turn
		<TT
CLASS="literal"
>Emit</TT
> all the way up. (<A
HREF="x4736.html#BSG.MAT.F.S68.803"
>Figure 58</A
>).
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.803"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass03.png"></P
></DIV
><P
><B
>Figure 58. Reflection Map</B
></P
></DIV
><P
>&#13;		6. This changes our first texture considerably. 
		In order to return the refraction texture to a nice blue
		tint, we have to add a new texture, leaving the texture type 
		set
		to <TT
CLASS="literal"
>None</TT
>. Select the <TT
CLASS="literal"
>Mix</TT
> 
		and <TT
CLASS="literal"
>Cmir</TT
>
		buttons, and set the <TT
CLASS="literal"
>Col</TT
> slider about 
		halfway up. Click
		the <TT
CLASS="literal"
>Neg</TT
> button and set the texture input 
		RGB sliders to a
		dark blue (<A
HREF="x4736.html#BSG.MAT.F.S68.804"
>Figure 59</A
>).
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.804"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass04.png"></P
></DIV
><P
><B
>Figure 59. Final touches</B
></P
></DIV
><P
>&#13;		The final result should look like <A
HREF="x4736.html#BSG.MAT.F.S68.805"
>Figure 60</A
>.
		The refraction effect is most noticeable when the scene is
		animated.
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.805"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass05.png"></P
></DIV
><P
><B
>Figure 60. Rendering</B
></P
></DIV
></DIV
><DIV
CLASS="section"
><H2
CLASS="section"
><A
NAME="section_materials_hollow_glass"
></A
>Hollow Glass</H2
><P
>&#13;		The procedure we've described above works fine for a solid 
		lump of glass, but how do we produce the appearance of hollow glass, like a 
		vase? 
	</P
><P
>&#13;		Thin glass has strong refraction only where it slopes away 
		from the
		eye at a steep angle. We can easily mimic this effect by using
		Blender's <TT
CLASS="literal"
>Blend</TT
> texture to control the 
		object's
		transparency, as well as another transparency texture to keep 
		the bright
		highlights visible.
	</P
><P
>&#13;		1. Add a new texture to the material. Select 
		<TT
CLASS="literal"
>Blend</TT
> as the
		type and select the <TT
CLASS="literal"
>Sphere</TT
> option.
	</P
><P
>&#13;		2. Return to the
		material buttons. Select <TT
CLASS="literal"
>Nor</TT
> as the mapping 
		type, and
		disable the X and Y axes in the input coordinates.
	</P
><P
>&#13;		3. <TT
CLASS="literal"
>Mix</TT
> the
		texture with <TT
CLASS="literal"
>Alpha</TT
>, then move the 
		<TT
CLASS="literal"
>Alpha</TT
> material
		slider to 0.0 and set the <TT
CLASS="literal"
>ZTransp</TT
> 
		option
		(<A
HREF="x4736.html#BSG.MAT.F.S68.806"
>Figure 61</A
>). 
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.806"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass06.png"></P
></DIV
><P
><B
>Figure 61. Setting transparency.</B
></P
></DIV
><P
>&#13;		This produces the effect of nice transparency as the surface 
		angles toward the eye,
		but we want the bright environment-mapped reflections to show 
		up on
		those otherwise-transparent areas. For example, if you look at 
		glass windows, you
		will see that bright light reflecting from the surface is 
		visible, preventing you from seeing through a pane that would otherwise be
		transparent. We can produce this effect easily by selecting 
		the environment-mapped
		reflection texture in the material window and enabling the
		<TT
CLASS="literal"
>Alpha</TT
> option (<A
HREF="x4736.html#BSG.MAT.F.S68.807"
>Figure 62</A
>). 
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.807"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass07.png"></P
></DIV
><P
><B
>Figure 62. Setting Reflections</B
></P
></DIV
><P
>&#13;		That's all there is to it. The result should look like
		<A
HREF="x4736.html#BSG.MAT.F.S68.808"
>Figure 63</A
>. 
	</P
><DIV
CLASS="figure"
><A
NAME="BSG.MAT.F.S68.808"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/materials/gfx/Glass08.png"></P
></DIV
><P
><B
>Figure 63. Hollow Glass</B
></P
></DIV
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