/**

 * $Id: texcache.c,v 1.1 2006-03-13 12:39:07 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 -1

static texcache_entry_index texcache_free_ptr;

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;

}