mirror of
https://github.com/brl/mutter.git
synced 2024-11-12 17:27:03 -05:00
a8fbde4710
This adds just some basic documentation to try and explain what CoglIndices are useful for. Reviewed-by: Neil Roberts <neil@linux.intel.com>
129 lines
4.3 KiB
C
129 lines
4.3 KiB
C
/*
|
|
* 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(CLUTTER_COMPILATION)
|
|
#error "Only <cogl/cogl.h> can be included directly."
|
|
#endif
|
|
|
|
#ifndef __COGL_INDICES_H__
|
|
#define __COGL_INDICES_H__
|
|
|
|
#include <cogl/cogl-index-buffer.h>
|
|
|
|
G_BEGIN_DECLS
|
|
|
|
/**
|
|
* SECTION:cogl-index-range
|
|
* @short_description: Fuctions for declaring a range of 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 squence 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.
|
|
*/
|
|
|
|
typedef struct _CoglIndices CoglIndices;
|
|
|
|
CoglIndices *
|
|
cogl_indices_new (CoglIndicesType type,
|
|
const void *indices_data,
|
|
int n_indices);
|
|
|
|
CoglIndices *
|
|
cogl_indices_new_for_buffer (CoglIndicesType type,
|
|
CoglIndexBuffer *buffer,
|
|
gsize offset);
|
|
|
|
CoglIndexBuffer *
|
|
cogl_indices_get_buffer (CoglIndices *indices);
|
|
|
|
CoglIndicesType
|
|
cogl_indices_get_type (CoglIndices *indices);
|
|
|
|
gsize
|
|
cogl_indices_get_offset (CoglIndices *indices);
|
|
|
|
void
|
|
cogl_indices_set_offset (CoglIndices *indices,
|
|
gsize offset);
|
|
|
|
CoglIndices *
|
|
cogl_get_rectangle_indices (int n_rectangles);
|
|
|
|
G_END_DECLS
|
|
|
|
#endif /* __COGL_INDICES_H__ */
|
|
|