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14<TITLE>Hardware Buffers In OGRE: The IndexData class</TITLE>
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37<H3> 2.7.1 The IndexData class </H3>
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39This class summarises the information required to use a set of indexes to render geometry. It's members are as follows:
40<DL COMPACT>
41<DT>indexStart
42<DD>The first index used by this piece of geometry; this can be useful for sharing a single index buffer among several geometry pieces.
43<DT>indexCount
44<DD>The number of indexes used by this particular renderable.
45<DT>indexBuffer
46<DD>The index buffer which is used to source the indexes.
47</DL>
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49
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51<H3> Creating an Index Buffer </H3>
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53Index buffers are created using See section <A HREF="vbo-update_4.html#SEC4">2.1 The Hardware Buffer Manager</A> just like vertex buffers, here's how:
54<TABLE><tr><td>&nbsp;</td><td class=example><pre>HardwareIndexBufferSharedPtr ibuf = HardwareBufferManager::getSingleton().
55        createIndexBuffer(
56                HardwareIndexBuffer::IT_16BIT, // type of index
57                numIndexes, // number of indexes
58                HardwareBuffer::HBU_STATIC_WRITE_ONLY, // usage
59                false); // no shadow buffer     
60</pre></td></tr></table>Once again, notice that the return type is a class rather than a pointer; this is reference counted so that the buffer is automatically destroyed when no more references are made to it. The parameters to the index buffer creation are:
61<DL COMPACT>
62<DT>indexType
63<DD>There are 2 types of index; 16-bit and 32-bit. They both perform the same way, except that the latter can address larger vertex buffers. If your buffer includes more than 65526 vertices, then you will need to use 32-bit indexes. Note that you should only use 32-bit indexes when you need to, since they incur more overhead than 16-bit vertices, and are not supported on some older hardware.
64<DT>numIndexes
65<DD>The number of indexes in the buffer. As with vertex buffers, you should consider whether you can use a shared index buffer which is used by multiple pieces of geometry, since there can be performance advantages to switching index buffers less often.
66<DT>usage
67<DD>This tells the system how you intend to use the buffer. See section <A HREF="vbo-update_5.html#SEC5">2.2 Buffer Usage</A>
68<DT>useShadowBuffer
69<DD>Tells the system whether you want this buffer backed by a system-memory copy. See section <A HREF="vbo-update_6.html#SEC6">2.3 Shadow Buffers</A>
70</DL>
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