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<h3 class="subsection"> 4.13.2 Mixmodes and Blending </h3>
<p>The <samp>‘mixmode’</samp> controls how a source (usually a texture) is blended on
top of the destination (usually a screen buffer). Typically mixmodes are set
on mesh factories or objects to control transparency of some kind.
There are various modes defined in <tt>‘include/ivideo/graph3d.h’</tt>.
</p>
<p>In the explanation below we use the following terms: <small>SRC</small> is the source of
the blend operation (usually the texture or material). <small>DST</small> is the
destination of the blend operation (usually the screen buffer or texture
on which you are rendering). <samp>‘srcAlpha’</samp> is the alpha component
of the source buffer. <samp>‘dstAlpha’</samp> is the alpha component of the destination
buffer. The following mixmodes are supported:
</p>
<ul>
<li> <samp>‘CS_FX_COPY’</samp>
Blending function: <small>SRC</small>. This mode is usually default. It simply
copies the source to the destination without blending.
</li><li> <samp>‘CS_FX_MULTIPLY’</samp>
Blending function: <small>SRC</small>*<small>DST</small>. This is a common blend mode to
simulate lighting.
</li><li> <samp>‘CS_FX_MULTIPLY2’</samp>
Blending function: 2*<small>SRC</small>*<small>DST</small>. This is a common blend mode
to simulate brighter lighting.
</li><li> <samp>‘CS_FX_ADD’</samp>
Blending function: <small>SRC</small>+<small>DST</small>. Add source and destination. This is a
mode that allows for nice transparency effects. One of the big advantages (as
opposed to <samp>‘alpha’</samp>) is that this mode doesn't require objects to be
sorted from back to front.
</li><li> <samp>‘CS_FX_ALPHA’</samp>
Blending function: <samp>‘alpha’</samp>*<small>SRC</small> + (1-<samp>‘alpha’</samp>)*<small>DST</small>.
The <samp>‘alpha’</samp> used in this formula is a combination of the <samp>‘srcAlpha’</samp>
and the alpha given in the alpha mask of the mixmode. But this
depends on the actual shader that is being used.
</li><li> <samp>‘CS_FX_SETALPHA(alpha)’</samp>
Convenience macro to set <samp>‘CS_FX_ALPHA’</samp> and set the alpha value to the
alpha mask (value is between 0 and 1).
</li><li> <samp>‘CS_FX_SETALPHA_INT(alpha)’</samp>
Convenience macro to set <samp>‘CS_FX_ALPHA’</samp> and set the alpha value to the
alpha mask (value is between 0 and 255).
</li><li> <samp>‘CS_FX_PREMULTALPHA’</samp>
Blending function: <small>SRC</small> + <small>DST</small>*(1-<samp>‘srcAlpha’</samp>). When the
source alpha component was multoplied into the source color then this acts
like normal alpha blending. If it was not then it acts like additive
blending. So this mixmode can be used to do both additive and alpha
blending on the same triangle and even interpolate between these two
extremes by appropriate choice of the color and alpha values.
</li><li> <samp>‘CS_FX_DESTALPHAADD’</samp>
Blending function: <samp>‘dstAlpha’</samp>*<small>SRC</small> + <small>DST</small>.
</li><li> <samp>‘CS_FX_SRCALPHAADD’</samp>
Blending function: <samp>‘srcAlpha’</samp>*<small>SRC</small> + <small>DST</small>.
</li><li> <samp>‘CS_FX_TRANSPARENT’</samp>
Blending function: <small>DST</small>. This mode will simply leave the destination
unchanged (fully transparent) except that the z-buffer is modified!
</li><li> <samp>‘CS_FX_MESH’</samp>
@@TODO
</li><li> <samp>‘CS_MIXMODE_ALPHATEST_AUTO’</samp>
@@TODO
</li><li> <samp>‘CS_MIXMODE_ALPHATEST_ENABLE’</samp>
@@TODO
</li><li> <samp>‘CS_MIXMODE_ALPHATEST_DISABLE’</samp>
@@TODO
</li></ul>
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