mutter/cogl/cogl-meta-texture.h

/*
 * Cogl
 *
 * An object oriented GL/GLES Abstraction/Utility Layer
 *
 * Copyright (C) 2011 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/>.
 *
 *
 */

#if !defined(__COGL_H_INSIDE__) && !defined(COGL_COMPILATION)
#error "Only <cogl/cogl.h> can be included directly."
#endif

#ifndef __COGL_META_TEXTURE_H__
#define __COGL_META_TEXTURE_H__

#include <cogl/cogl-pipeline-layer-state.h>

COGL_BEGIN_DECLS

/**
 * SECTION:cogl-meta-texture
 * @short_description: Interface for high-level textures built from
 *                     low-level textures like #CoglTexture2D and
 *                     #CoglTexture3D.
 *
 * Cogl helps to make it easy to deal with high level textures such
 * as #CoglAtlasTexture<!-- -->s, #CoglSubTexture<!-- -->s,
 * #CoglTexturePixmapX11 textures and #CoglTexture2DSliced textures
 * consistently.
 *
 * A #CoglMetaTexture is a texture that might internally be
 * represented by one or more low-level #CoglTexture<!-- -->s
 * such as #CoglTexture2D or #CoglTexture3D. These low-level textures
 * are the only ones that a GPU really understands but because
 * applications often want more high-level texture abstractions
 * (such as storing multiple textures inside one larger "atlas"
 * texture) it's desirable to be able to deal with these
 * using a common interface.
 *
 * For example the GPU is not able to automatically handle repeating a
 * texture that is part of a larger atlas texture but if you use
 * %COGL_PIPELINE_WRAP_MODE_REPEAT with an atlas texture when drawing
 * with cogl_rectangle() you should see that it "Just Works™" - at
 * least if you don't use multi-texturing. The reason this works is
 * because cogl_rectangle() internally understands the #CoglMetaTexture
 * interface and is able to manually resolve the low-level textures
 * using this interface and by making multiple draw calls it can
 * emulate the texture repeat modes.
 *
 * Cogl doesn't aim to pretend that meta-textures are just like real
 * textures because it would get extremely complex to try and emulate
 * low-level GPU semantics transparently for these textures.  The low
 * level drawing APIs of Cogl, such as cogl_primitive_draw() don't
 * actually know anything about the #CoglMetaTexture interface and its
 * the developer's responsibility to resolve all textures referenced
 * by a #CoglPipeline to low-level textures before drawing.
 *
 * If you want to develop custom primitive APIs like
 * cogl_framebuffer_draw_rectangle() and you want to support drawing
 * with #CoglAtlasTexture<!-- -->s or #CoglSubTexture<!-- -->s for
 * example, then you will need to use this #CoglMetaTexture interface
 * to be able to resolve high-level textures into low-level textures
 * before drawing with Cogl's low-level drawing APIs such as
 * cogl_primitive_draw().
 *
 * <note>Most developers won't need to use this interface directly
 * but still it is worth understanding the distinction between
 * low-level and meta textures because you may find other references
 * in the documentation that detail limitations of using
 * meta-textures.</note>
 */

#ifdef __COGL_H_INSIDE__
/* For the public C api we typedef interface types as void to avoid needing
 * lots of casting in code and instead we will rely on runtime type checking
 * for these objects. */
typedef void CoglMetaTexture;
#else
typedef struct _CoglMetaTexture CoglMetaTexture;
#define COGL_META_TEXTURE(X) ((CoglMetaTexture *)X)
#endif

/**
 * CoglMetaTextureCallback:
 * @sub_texture: A low-level #CoglTexture making up part of a
 *               #CoglMetaTexture.
 * @sub_texture_coords: A float 4-tuple ordered like
 *                      (tx1,ty1,tx2,ty2) defining what region of the
 *                      current @sub_texture maps to a sub-region of a
 *                      #CoglMetaTexture. (tx1,ty1) is the top-left
 *                      sub-region coordinate and (tx2,ty2) is the
 *                      bottom-right. These are low-level texture
 *                      coordinates.
 * @meta_coords: A float 4-tuple ordered like (tx1,ty1,tx2,ty2)
 *               defining what sub-region of a #CoglMetaTexture this
 *               low-level @sub_texture maps too. (tx1,ty1) is
 *               the top-left sub-region coordinate and (tx2,ty2) is
 *               the bottom-right. These are high-level meta-texture
 *               coordinates.
 * @user_data: A private pointer passed to
 *             cogl_meta_texture_foreach_in_region().
 *
 * A callback used with cogl_meta_texture_foreach_in_region() to
 * retrieve details of all the low-level #CoglTexture<!-- -->s that
 * make up a given #CoglMetaTexture.
 *
 * Since: 1.10
 * Stability: unstable
 */
typedef void (*CoglMetaTextureCallback) (CoglTexture *sub_texture,
                                         const float *sub_texture_coords,
                                         const float *meta_coords,
                                         void *user_data);

/**
 * cogl_meta_texture_foreach_in_region:
 * @meta_texture: An object implementing the #CoglMetaTexture
 *                interface.
 * @tx_1: The top-left x coordinate of the region to iterate
 * @ty_1: The top-left y coordinate of the region to iterate
 * @tx_2: The bottom-right x coordinate of the region to iterate
 * @ty_2: The bottom-right y coordinate of the region to iterate
 * @wrap_s: The wrap mode for the x-axis
 * @wrap_t: The wrap mode for the y-axis
 * @callback: A #CoglMetaTextureCallback pointer to be called
 *            for each low-level texture within the specified region.
 * @user_data: A private pointer that is passed to @callback.
 *
 * Allows you to manually iterate the low-level textures that define a
 * given region of a high-level #CoglMetaTexture.
 *
 * For example cogl_texture_2d_sliced_new_with_size() can be used to
 * create a meta texture that may slice a large image into multiple,
 * smaller power-of-two sized textures. These high level textures are
 * not directly understood by a GPU and so this API must be used to
 * manually resolve the underlying textures for drawing.
 *
 * All high level textures (#CoglAtlasTexture, #CoglSubTexture,
 * #CoglTexturePixmapX11, and #CoglTexture2DSliced) can be handled
 * consistently using this interface which greately simplifies
 * implementing primitives that support all texture types.
 *
 * For example if you use the cogl_rectangle() API then Cogl will
 * internally use this API to resolve the low level textures of any
 * meta textures you have associated with CoglPipeline layers.
 *
 * <note>The low level drawing APIs such as cogl_primitive_draw()
 * don't understand the #CoglMetaTexture interface and so it is your
 * responsibility to use this API to resolve all CoglPipeline textures
 * into low-level textures before drawing.</note>
 *
 * For each low-level texture that makes up part of the given region
 * of the @meta_texture, @callback is called specifying how the
 * low-level texture maps to the original region.
 *
 * Since: 1.10
 * Stability: unstable
 */
void
cogl_meta_texture_foreach_in_region (CoglMetaTexture *meta_texture,
                                     float tx_1,
                                     float ty_1,
                                     float tx_2,
                                     float ty_2,
                                     CoglPipelineWrapMode wrap_s,
                                     CoglPipelineWrapMode wrap_t,
                                     CoglMetaTextureCallback callback,
                                     void *user_data);

COGL_END_DECLS

#endif /* __COGL_META_TEXTURE_H__ */