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/*
* Cogl
*
* An object oriented GL/GLES Abstraction/Utility Layer
*
* Copyright (C) 2010 Intel Corporation.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library. If not, see <http://www.gnu.org/licenses/>.
*
*
*
* Authors:
* Robert Bragg <robert@linux.intel.com>
*/
#if !defined(__COGL_H_INSIDE__) && !defined(COGL_COMPILATION)
#error "Only <cogl/cogl.h> can be included directly."
#endif
#ifndef __COGL_INDICES_H__
#define __COGL_INDICES_H__
/* We forward declare the CoglIndices type here to avoid some circular
* dependency issues with the following headers.
*/
typedef struct _CoglIndices CoglIndices;
#include <cogl/cogl-index-buffer.h>
COGL_BEGIN_DECLS
/**
* SECTION:cogl-indices
* @short_description: Describe vertex indices stored in a #CoglIndexBuffer.
*
* Indices allow you to avoid duplicating vertices in your vertex data
* by virtualizing your data and instead providing a sequence of index
* values that tell the GPU which data should be used for each vertex.
*
* If the GPU is given a sequence of indices it doesn't simply walk
* through each vertex of your data in order it will instead walk
* through the indices which can provide random access to the
* underlying data.
*
* Since it's very common to have duplicate vertices when describing a
* shape as a list of triangles it can often be a significant space
* saving to describe geometry using indices. Reducing the size of
* your models can make it cheaper to map them into the GPU by
* reducing the demand on memory bandwidth and may help to make better
* use of your GPUs internal vertex caching.
*
* For example, to describe a quadrilateral as 2 triangles for the GPU
* you could either provide data with 6 vertices or instead with
* indices you can provide vertex data for just 4 vertices and an
* index buffer that specfies the 6 vertices by indexing the shared
* vertices multiple times.
*
* |[
* CoglVertex2f quad_vertices[] = {
* {x0, y0}, //0 = top left
* {x1, y1}, //1 = bottom left
* {x2, y2}, //2 = bottom right
* {x3, y3}, //3 = top right
* };
* //tell the gpu how to interpret the quad as 2 triangles...
* unsigned char indices[] = {0, 1, 2, 0, 2, 3};
* ]|
*
* Even in the above illustration we see a saving of 10bytes for one
* quad compared to having data for 6 vertices and no indices but if
* you need to draw 100s or 1000s of quads then its really quite
* significant.
*
* Something else to consider is that often indices can be defined
* once and remain static while the vertex data may change for
* animations perhaps. That means you may be able to ignore the
* negligable cost of mapping your indices into the GPU if they don't
* ever change.
*
* The above illustration is actually a good example of static indices
* because it's really common that developers have quad mesh data that
* they need to display and we know exactly what that indices array
* needs to look like depending on the number of quads that need to be
* drawn. It doesn't matter how the quads might be animated and
* changed the indices will remain the same. Cogl even has a utility
* (cogl_get_rectangle_indices()) to get access to re-useable indices
* for drawing quads as above.
*/
CoglIndices *
cogl_indices_new (CoglContext *context,
CoglIndicesType type,
const void *indices_data,
int n_indices);
CoglIndices *
cogl_indices_new_for_buffer (CoglIndicesType type,
CoglIndexBuffer *buffer,
size_t offset);
CoglIndexBuffer *
cogl_indices_get_buffer (CoglIndices *indices);
CoglIndicesType
cogl_indices_get_type (CoglIndices *indices);
size_t
cogl_indices_get_offset (CoglIndices *indices);
void
cogl_indices_set_offset (CoglIndices *indices,
size_t offset);
CoglIndices *
cogl_get_rectangle_indices (CoglContext *context, int n_rectangles);
/**
* cogl_is_indices:
* @object: A #CoglObject pointer
*
* Gets whether the given object references a #CoglIndices.
*
* Return value: %TRUE if the object references a #CoglIndices
* and %FALSE otherwise.
* Since: 1.10
* Stability: unstable
*/
CoglBool
cogl_is_indices (void *object);
COGL_END_DECLS
#endif /* __COGL_INDICES_H__ */
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