/**

  * $Id: texcache.c,v 1.2 2006-03-14 13:02:06 nkeynes Exp $

  *

  * Texture cache. Responsible for maintaining a working set of OpenGL 

  * textures. 

  *

  *

  * Copyright (c) 2005 Nathan Keynes.

  *

  * This program is free software; you can redistribute it and/or modify

  * it under the terms of the GNU General Public License as published by

  * the Free Software Foundation; either version 2 of the License, or

  * (at your option) any later version.

  *

  * This program 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 General Public License for more details.

  */

 #include <assert.h>

 #include "pvr2/pvr2.h"

 /** Specifies the maximum number of OpenGL

  * textures we're willing to have open at a time. If more are

  * needed, textures will be evicted in LRU order.

  */

 #define MAX_TEXTURES 64

 /**

  * Data structure:

  *

  * Main operations:

  *    find entry by texture_addr

  *    add new entry

  *    move entry to tail of lru list

  *    remove entry

  */

 typedef signed short texcache_entry_index;

 #define EMPTY_ENTRY 0xFF

 static texcache_entry_index texcache_free_ptr = 0;

 static GLuint texcache_free_list[MAX_TEXTURES];

 typedef struct texcache_entry {

     uint32_t texture_addr;

     int width, height, mode;

     GLuint texture_id;

     texcache_entry_index next;

     uint32_t lru_count;

 } *texcache_entry_t;

 static uint8_t texcache_page_lookup[PVR2_RAM_PAGES];

 static uint32_t texcache_active_ptr;

 static uint32_t texcache_ref_counter;

 static struct texcache_entry texcache_active_list[MAX_TEXTURES];

 /**

  * Initialize the texture cache. Note that the GL context must have been

  * initialized before calling this function.

  */

 void texcache_init( )

 {

     int i;

     GLuint texids[MAX_TEXTURES];

     glGenTextures( MAX_TEXTURES, texids );

     for( i=0; i<PVR2_RAM_PAGES; i++ ) {

 	texcache_page_lookup[i] = EMPTY_ENTRY;

     }

     for( i=0; i<MAX_TEXTURES; i++ ) {

 	texcache_active_list[i].texture_id = texids[i];

 	texcache_free_list[i] = i;

     }

     texcache_free_ptr = 0;

     texcache_ref_counter = 0;

 }

 /**

  * Flush all textures from the cache, returning them to the free list.

  */

 void texcache_flush( )

 {

     int i;

     /* clear structures */

     for( i=0; i<PVR2_RAM_PAGES; i++ ) {

 	texcache_page_lookup[i] = EMPTY_ENTRY;

     }

     for( i=0; i<MAX_TEXTURES; i++ ) {

 	texcache_free_list[i] = i;

     }

     texcache_free_ptr = 0;

     texcache_ref_counter = 0;

 }

 /**

  * Flush all textures and delete. The cache will be non-functional until

  * the next call to texcache_init(). This would typically be done if

  * switching GL targets.

  */    

 void texcache_shutdown( )

 {

     GLuint texids[MAX_TEXTURES];

     int i;

     texcache_flush();

     for( i=0; i<MAX_TEXTURES; i++ ) {

 	texids[i] = texcache_active_list[i].texture_id;

     }

     glDeleteTextures( MAX_TEXTURES, texids );

 }

 /**

  * Evict all textures contained in the page identified by a texture address.

  */

 void texcache_invalidate_page( uint32_t texture_addr ) {

     uint32_t texture_page = texture_addr >> 12;

     texcache_entry_index idx = texcache_page_lookup[texture_page];

     if( idx == EMPTY_ENTRY )

 	return;

     assert( texcache_free_ptr >= 0 );

     do {

 	texcache_entry_t entry = &texcache_active_list[idx];	

 	/* release entry */

 	texcache_free_ptr--;

 	texcache_free_list[texcache_free_ptr] = idx;

 	idx = entry->next;

 	entry->next = EMPTY_ENTRY;

     } while( idx != EMPTY_ENTRY );

     texcache_page_lookup[texture_page] = EMPTY_ENTRY;

 }

 /**

  * Evict a single texture from the cache.

  * @return the slot of the evicted texture.

  */

 static texcache_entry_index texcache_evict( void )

 {

     /* Full table scan - take over the entry with the lowest lru value */

     texcache_entry_index slot = 0;

     int lru_value = texcache_active_list[0].lru_count;

     int i;

     for( i=1; i<MAX_TEXTURES; i++ ) {

 	/* FIXME: account for rollover */

 	if( texcache_active_list[i].lru_count < lru_value ) {

 	    slot = i;

 	    lru_value = texcache_active_list[i].lru_count;

 	}

     }

     /* Remove the selected slot from the lookup table */

     uint32_t evict_page = texcache_active_list[slot].texture_addr;

     texcache_entry_index replace_next = texcache_active_list[slot].next;

     texcache_active_list[slot].next = EMPTY_ENTRY; /* Just for safety */

     if( texcache_page_lookup[evict_page] == slot ) {

 	texcache_page_lookup[evict_page] = replace_next;

     } else {

 	texcache_entry_index idx = texcache_page_lookup[evict_page];

 	texcache_entry_index next;

 	do {

 	    next = texcache_active_list[idx].next;

 	    if( next == slot ) {

 		texcache_active_list[idx].next = replace_next;

 		break;

 	    }

 	    idx = next;

 	} while( next != EMPTY_ENTRY );

     }

     return slot;

 }

 /**

  * Load texture data from the given address and parameters into the currently

  * bound OpenGL texture.

  */

 static texcache_load_texture( uint32_t texture_addr, int width, int height,

 			      int mode ) {

     uint32_t bytes = width * height;

     int bpp = 2;

     GLint intFormat, format, type;

     switch( mode & PVR2_TEX_FORMAT_MASK ) {

     case PVR2_TEX_FORMAT_ARGB1555:

 	bytes <<= 1;

 	intFormat = GL_RGB5_A1;

 	format = GL_RGBA;

 	type = GL_UNSIGNED_SHORT_5_5_5_1;

 	break;

     case PVR2_TEX_FORMAT_RGB565:

 	bytes <<= 1;

 	intFormat = GL_RGBA;

 	format = GL_RGBA;

 	type = GL_UNSIGNED_SHORT_5_6_5;

 	break;

     case PVR2_TEX_FORMAT_ARGB4444:

 	bytes <<= 1;

 	intFormat = GL_RGBA4;

 	format = GL_RGBA;

 	type = GL_UNSIGNED_SHORT_4_4_4_4;

 	break;

     case PVR2_TEX_FORMAT_YUV422:

 	ERROR( "YUV textures not supported" );

 	break;

     case PVR2_TEX_FORMAT_BUMPMAP:

 	ERROR( "Bumpmap not supported" );

 	break;

     case PVR2_TEX_FORMAT_IDX4:

 	/* Supported? */

 	bytes >>= 1;

 	intFormat = GL_INTENSITY4;

 	format = GL_COLOR_INDEX;

 	type = GL_UNSIGNED_BYTE;

 	bpp = 0;

 	break;

     case PVR2_TEX_FORMAT_IDX8:

 	intFormat = GL_INTENSITY8;

 	format = GL_COLOR_INDEX;

 	type = GL_UNSIGNED_BYTE;

 	bpp = 1;

 	break;

     }

     unsigned char data[bytes];

     /* load data from image, detwiddling/uncompressing as required */

     if( PVR2_TEX_IS_COMPRESSED(mode) ) {

 	ERROR( "VQ Compression not supported" );

     } else {

 	pvr2_vram64_read( &data, texture_addr, bytes );

 	if( PVR2_TEX_IS_TWIDDLED(mode) ) {

 	    /* Untwiddle */

 	}

     }

     /* Pass to GL */

     glTexImage2D( GL_TEXTURE_2D, 0, intFormat, width, height, 0, format, type,

 		  data );

 }

 /**

  * Return a texture ID for the texture specified at the supplied address

  * and given parameters (the same sequence of bytes could in theory have

  * multiple interpretations). We use the texture address as the primary

  * index, but allow for multiple instances at each address. The texture

  * will be bound to the GL_TEXTURE_2D target before being returned.

  * 

  * If the texture has already been bound, return the ID to which it was

  * bound. Otherwise obtain an unused texture ID and set it up appropriately.

  */

 GLuint texcache_get_texture( uint32_t texture_addr, int width, int height,

 			     int mode )

 {

     uint32_t texture_page = texture_addr >> 12;

     texcache_entry_index idx = texcache_page_lookup[texture_page];

     while( idx != EMPTY_ENTRY ) {

 	texcache_entry_t entry = &texcache_active_list[idx];

 	if( entry->texture_addr == texture_addr &&

 	    entry->mode == mode &&

 	    entry->width == width &&

 	    entry->height == height ) {

 	    entry->lru_count = texcache_ref_counter++;

 	    glBindTexture( GL_TEXTURE_2D, entry->texture_id );

 	    return entry->texture_id;

 	}

         idx = entry->next;

     }

     /* Not found - check the free list */

     int slot = 0;

     if( texcache_free_ptr < MAX_TEXTURES ) {

 	slot = texcache_free_list[texcache_free_ptr++];

     } else {

 	slot = texcache_evict();

     }

     /* Construct new entry */

     texcache_active_list[slot].texture_addr = texture_addr;

     texcache_active_list[slot].width = width;

     texcache_active_list[slot].height = height;

     texcache_active_list[slot].mode = mode;

     texcache_active_list[slot].lru_count = texcache_ref_counter++;

     /* Add entry to the lookup table */

     texcache_active_list[slot].next = texcache_page_lookup[texture_page];

     texcache_page_lookup[texture_page] = slot;

     /* Construct the GL texture */

     GLuint texid = texcache_free_list[texcache_free_ptr++];

     glBindTexture( GL_TEXTURE_2D, texid );

     texcache_load_texture( texture_addr, width, height, mode );

     return texcache_active_list[slot].texture_id;

 }