/* LICENSE BLOCK
Part of mde: a Modular D game-oriented Engine
Copyright © 2007-2008 Diggory Hardy

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.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>. */

/** Font caching system.
 *
 * This module also serves as the internals to the font module and shouldn't be used except through
 * the font module. The two modules could be combined, at a cost to readability.
 *
 * Three types of coordinates get used in the system: FreeType coordinates for each glyph, texture
 * coordinates, and OpenGL's model/world coordinates (for rendering). The freetype and texture
 * coords are cartesian (i.e. y increases upwards), although largely this is too abstract to
 * matter. However, for the model/world coords, y increases downwards. */
module mde.font.FontTexture;

import mde.types.Colour;
import mde.content.AStringContent;
import mde.font.exception;

import derelict.freetype.ft;
import derelict.opengl.gl;

import Utf = tango.text.convert.Utf;
import tango.util.log.Log : Log, Logger;

private Logger logger;
static this () {
    logger = Log.getLogger ("mde.font.FontTexture");
}

static const int dimW = 256, dimH = 256;	// Texture size
const wFactor = 1f / dimW;
const hFactor = 1f / dimH;

/** A FontTexture is basically a cache of all font glyphs rendered so far.
  *
  * This class should be limited to code for rendering to (and otherwise handling) textures and
  * rendering fonts to the screen.
  *
  * Technically, there's no reason it shouldn't be a static part of the FontStyle class. */
class FontTexture
{
    // Call if font(s) have been changed and glyphs must be recached.
    void clear () {
        foreach (t; tex) {
            glDeleteTextures (1, &(t.texID));
        }
        cachedGlyphs = null;
        ++cacheVer;
    }
    
    /** Cache informatation for rendering a block of text.
     *
     * Recognises '\r', '\n' and "\r\n" as end-of-line markers. */
    void updateCache (FT_Face face, char[] str, ref TextBlock cache)
    {
        debug scope (failure)
                logger.error ("updateCache failed");
        
        if (cache.cacheVer == cacheVer)	// Existing cache is up-to-date
            return;
        
        cache.cacheVer = cacheVer;
	cache.w = cache.h = 0;		// reset
        
        /* Convert the string to an array of character codes (which is equivalent to decoding UTF8
        * to UTF32 since no character code is ever > dchar.max). */
        static dchar[] chrs;	// keep memory for future calls (NOTE: change for threading)
        chrs = Utf.toString32 (str, chrs);
        
        // Allocate space.
        // Since end-of-line chars get excluded, will often be slightly larger than necessary.
        cache.chars.length = chrs.length;
        cache.chars.length = 0;
        
        int lineSep = face.size.metrics.height >> 6;
        bool hasKerning = (FT_HAS_KERNING (face) != 0);
        int y = face.size.metrics.ascender >> 6;
        CharCache cc;		// struct; reused for each character
        
        for (size_t i = 0; i < chrs.length; ++i)
        {
            // For each line:
            int x = 0;	// x pos for next glyph
            uint gi_prev = 0;	// previous glyph index (needed for kerning)
            
            for (; i < chrs.length; ++i)
            {
                // If end-of-line, break to find yMax for next line.
                if (chrs.length >= i+2 && chrs[i..i+2] == "\r\n"d) {
                    ++i;
                    break;
                }
                if (chrs[i] == '\n' || chrs[i] == '\r') {
                    break;
                }
                
                cc.ga = chrs[i] in cachedGlyphs;
                if (cc.ga is null) {                    // Not cached
                    addGlyph (face, chrs[i]);           // so render it
                    cc.ga = chrs[i] in cachedGlyphs;    // get the ref of the copy we've stored
                    assert (cc.ga !is null, "Unable to cache glyph!");
                }
                
                // Kerning
                if (hasKerning && (gi_prev != 0)) {
                    FT_Vector delta;
                    FT_Get_Kerning (face, gi_prev, cc.ga.index, FT_Kerning_Mode.FT_KERNING_DEFAULT, &delta);
                    x += delta.x >> 6;
                }
                
                // ga.left component: adding this slightly improves glyph layout. Note that the
                // left-most glyph on a line may not start right on the edge, but this looks best.
                cc.xPos = x + cc.ga.left;
                cc.yPos = y - cc.ga.top;
                x += cc.ga.advanceX;
                
                cache.chars ~= cc;
                
                // Update rect total size. Top and left coords should be zero, so make width and
                // height maximal x and y coordinates.
                if (cc.xPos + cc.ga.w > cache.w)
                    cache.w = cc.xPos + cc.ga.w;
                /+if (cc.yPos + cc.ga.h > cache.h)
                    cache.h = cc.yPos + cc.ga.h;+/
            }
            // Now increment i and continue with the next line if there is one.
            y += lineSep;
            cache.h += lineSep;
        }
    }
    
    /** Render a block of text using a cache. Updates the cache if necessary.
     *
     * Params:
     *  face =	Current typeface pointer; must be passed from font.d (only needed if the cache is
     *  	invalid)
     *  str =	Text to render (only needed if the cache is invalid)
     *  cache =	Cache used to speed up CPU-side rendering code
     *  x =	Smaller x-coordinate of position
     *  y =	Smaller y-coordinate of position
     *  col =	Text colour (note: currently limited to black or white)
     *  index =	Index of edit position, or size_t.max if no idet position. */
    void drawCache (FT_Face face, char[] str, ref TextBlock cache, int x, int y, Colour col, size_t index) {
        updateCache (face, str, cache);	// update if necessary
        debug scope (failure)
                logger.error ("drawTextCache failed");
        
        // opaque (GL_DECAL would be equivalent)
        glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
        
        drawCacheImpl (face, cache, x, y, col, index);
    }
    /** A variation of drawCache, for transparent text.
     *
     * Instead of passing the alpha value(s) as arguments, set the openGL colour prior to calling:
     * ---
     * glColor3f (.5f, .5f, .5f);	// set alpha to half
     * drawCacheA (face, ...);
     * 
     * glColor3ub (0, 255, 127);	// alpha 0 for red, 1 for green, half for blue
     * drawCacheA (face, ...);
     * ---
     *
     * The overhead of the transparency is minimal. */
    void drawCacheA (FT_Face face, char[] str, ref TextBlock cache, int x, int y, Colour col, size_t index) {
        updateCache (face, str, cache);	// update if necessary
        debug scope (failure)
                logger.error ("drawTextCache failed");
        
        // transparency alpha
        // alpha is current colour, per component
        glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
        
	drawCacheImpl (face, cache, x, y, col, index);
    }
    
    private void drawCacheImpl (FT_Face face, ref TextBlock cache, int x, int y, Colour col, size_t index) {
        if (DerelictGL.availableVersion() >= GLVersion.Version14) {
            glBlendFunc (GL_CONSTANT_COLOR, GL_ONE_MINUS_SRC_COLOR);
            glBlendColor(col.r, col.g, col.b, 1f);	// text colour
        } else
            glBlendFunc (col.nearestGLConst, GL_ONE_MINUS_SRC_COLOR);
        
        glEnable (GL_TEXTURE_2D);
        glEnable(GL_BLEND);
        
        foreach (chr; cache.chars) {
            GlyphAttribs* ga = chr.ga;
            
            glBindTexture(GL_TEXTURE_2D, ga.texID);
            
            int x1 = x + chr.xPos;
            int y1 = y + chr.yPos;
            int x2 = x1 + ga.w;
            int y2 = y1 + ga.h;
            float tx1 = ga.x * wFactor;
            float ty1 = ga.y * hFactor;
            float tx2 = (ga.x + ga.w) * wFactor;
            float ty2 = (ga.y + ga.h) * hFactor;
           
            glBegin (GL_QUADS);
            glTexCoord2f (tx1, ty1);	glVertex2i (x1, y1);
            glTexCoord2f (tx2, ty1);	glVertex2i (x2, y1);
            glTexCoord2f (tx2, ty2);	glVertex2i (x2, y2);
            glTexCoord2f (tx1, ty2);	glVertex2i (x1, y2);
            glEnd ();
        }
	glDisable(GL_TEXTURE_2D);
        glDisable(GL_BLEND);
	
	if (index <= cache.chars.length) {	// draw edit position
	    int x1;
	    if (index == 0)
		x1 = x + 1;
	    else {
		auto c = cache.chars[index-1];
		x1 = x + c.xPos + c.ga.advanceX;
	    }
	    glColor3f(col.r, col.g, col.b);
	    glRecti(x1 - 1, y, x1, y + (face.size.metrics.height >> 6));
	}
    }
    
    void addGlyph (FT_Face face, dchar chr) {
        debug scope (failure)
                logger.error ("FontTexture.addGlyph failed!");
        
        auto gi = FT_Get_Char_Index (face, chr);
        auto g = face.glyph;
        
        if (FT_Load_Glyph (face, gi, FT_LOAD_RENDER | fontOpts.modeFlag))
            throw new fontGlyphException ("Unable to render glyph");
        
        auto b = g.bitmap;
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        //glPixelStorei (GL_UNPACK_ROW_LENGTH, b.pitch);
        
        GlyphAttribs ga;
        ga.w		= b.width;
        ga.h		= b.rows;
        ga.left		= g.bitmap_left;
        ga.top		= g.bitmap_top;
        ga.advanceX	= g.advance.x >> 6;
        ga.index	= gi;
        if (b.pixel_mode == FT_Pixel_Mode.FT_PIXEL_MODE_LCD)
            ga.w /= 3;
        if (b.pixel_mode == FT_Pixel_Mode.FT_PIXEL_MODE_LCD_V)
            ga.h /= 3;
        
        foreach (ref t; tex) {
            if (t.addGlyph (ga))
                goto gotTexSpace;
        }
        // if here, no existing texture had the room for the glyph so create a new texture
        // NOTE: check if using more than one texture impacts performance due to texture switching
        debug logger.trace ("Creating a new font texture.");
        tex ~= TexPacker.create();
        assert (tex[$-1].addGlyph (ga), "Failed to fit glyph in a new texture but addGlyph didn't throw");
        
        gotTexSpace:
        glBindTexture(GL_TEXTURE_2D, ga.texID);
        GLenum format;
        ubyte[] buffer;	// use our own pointer, since for LCD modes we need to perform a conversion
        if (b.pixel_mode == FT_Pixel_Mode.FT_PIXEL_MODE_GRAY && b.num_grays == 256) {
            assert (b.pitch == b.width, "Have assumed b.pitch == b.width for gray glyphs.");
            buffer = b.buffer[0..b.pitch*b.rows];
            format = GL_LUMINANCE;
        } else if (b.pixel_mode == FT_Pixel_Mode.FT_PIXEL_MODE_LCD) {
            // NOTE: Can't seem to get OpenGL to read freetype's RGB buffers properly, so convent.
            /* NOTE: Sub-pixel rendering probably also needs filtering. I haven't tried, since it's
             * disabled in my build of the library. For a tutorial on the filtering, see:
             * http://dmedia.dprogramming.com/?n=Tutorials.TextRendering1 */
            buffer = new ubyte[b.width*b.rows];
            for (uint i = 0; i < b.rows; ++i)
                for (uint j = 0; j < b.width; j+= 3)
            {
                buffer[i*b.width + j + 0] = b.buffer[i*b.pitch + j + 0];
                buffer[i*b.width + j + 1] = b.buffer[i*b.pitch + j + 1];
                buffer[i*b.width + j + 2] = b.buffer[i*b.pitch + j + 2];
            }
            
            format = (fontOpts.mode() >= 4) ? GL_BGR : GL_RGB;
        } else if (b.pixel_mode == FT_Pixel_Mode.FT_PIXEL_MODE_LCD_V) {
            // NOTE: Notes above apply. But in this case converting the buffers seems essential.
            buffer = new ubyte[b.width*b.rows];
            for (uint i = 0; i < b.rows; ++i)
                for (uint j = 0; j < b.width; ++j)
            {
                // i/3 is the "real" row, b.width*3 is our width (with subpixels), j is column,
                // i%3 is sub-pixel (R/G/B). i/3*3 necessary to round to multiple of 3
                buffer[i/3*b.width*3 + 3*j + i%3] = b.buffer[i*b.pitch + j];
            }
            
            format = (fontOpts.mode() >= 4) ? GL_BGR : GL_RGB;
        } else
            throw new fontGlyphException ("Unsupported freetype bitmap format");
        
        glTexSubImage2D(GL_TEXTURE_2D, 0,
                        ga.x, ga.y,
                        ga.w, ga.h,
                        format, GL_UNSIGNED_BYTE,
                        cast(void*) buffer.ptr);
        
        cachedGlyphs[chr] = ga;
    }
    
    // Draw the first glyph cache texture in the upper-left corner of the screen.
    debug (drawGlyphCache) void drawTexture () {
        if (tex.length == 0) return;
        glEnable (GL_TEXTURE_2D);
        glBindTexture(GL_TEXTURE_2D, tex[0].texID);
        glEnable(GL_BLEND);
        glBlendFunc (GL_ONE, GL_ONE_MINUS_SRC_COLOR);
        float[4] Cc = [ 1.0f, 1f, 1f, 1f ];
        glTexEnvfv(GL_TEXTURE_ENV, GL_TEXTURE_ENV_COLOR, Cc.ptr);
        
        glBegin (GL_QUADS);
        glTexCoord2f (0f, 0f);	glVertex2i (0, 0);
        glTexCoord2f (1f, 0f);	glVertex2i (dimW, 0);
        glTexCoord2f (1f, 1f);	glVertex2i (dimW, dimH);
        glTexCoord2f (0f, 1f);	glVertex2i (0, dimH);
        glEnd ();
        
        glDisable(GL_TEXTURE_2D);
        glDisable(GL_BLEND);
    }
    
private:
    TexPacker[] tex;	// contains the gl texture id and packing data
    
    GlyphAttribs[dchar]	cachedGlyphs;
    int cacheVer = 0;	// version of cache, used to make sure TextBlock caches are current.
}

// Use LinePacker for our texture packer:
alias LinePacker TexPacker;

/** Represents one gl texture; packs glyphs into lines. */
struct LinePacker
{
    // create a new texture
    static LinePacker create () {
        LinePacker p;
        //FIXME (gl): why do I get a blank texture when binding to non-0?
        //glGenTextures (1, &(p.texID));
        p.texID = 0;
        
        // add a pretty background to the texture
        debug (drawGlyphCache) {
            glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
            glPixelStorei (GL_UNPACK_ROW_LENGTH, 0);
            ubyte[3][dimH][dimW] testTex;
            for (size_t i = 0; i < dimW; ++i)
                for (size_t j = 0; j < dimH; ++j)
            {
                testTex[i][j][0] = cast(ubyte) (i + j);
                testTex[i][j][1] = cast(ubyte) i;
                testTex[i][j][2] = cast(ubyte) j;
            }
            void* ptr = testTex.ptr;
        } else
            const void* ptr = null;
        
        // Create a texture without initialising values.
        glBindTexture(GL_TEXTURE_2D, p.texID);
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB,
                     dimW, dimH, 0,
                     GL_RGB, GL_UNSIGNED_BYTE, ptr);
        return p;
    }
    
    /** Find space for a glyph of size attr.w, attr.h within the texture.
     *
     * Throws: fontGlyphException if glyph dimensions are larger than the texture.
     *
     * Returns false if unable to fit the glyph into the texture, true if successful. If
     * successful, attr's x and y are set to suitible positions such that the rect given by attr's
     * x, y, w & h is a valid subregion of the texture. */
    bool addGlyph (ref GlyphAttribs attr) {
        if (attr.w > dimW || attr.h > dimH)
            throw new fontGlyphException ("Glyph too large to fit texture!");
        
        attr.texID = texID;		// Set now. Possibly reset if new texture is needed.
        if (attr.w == 0) return true;	// 0 sized glyph; x and y are unimportant.
        
        bool cantFitExtraLine = nextYPos + attr.h >= dimH;
        foreach (ref line; lines) {
            if (line.length + attr.w <= dimW &&		// if sufficient length and
                line.height >= attr.h &&		// sufficient height and
                (cantFitExtraLine ||			// either there's not room for another line
                line.height <= attr.h * WASTE_H))	// or we're not wasting much vertical space
            {						// then use this line
                attr.x = line.length;
                attr.y = line.yPos;
                attr.texID = texID;
                line.length += attr.w;
                return true;
            }
        }
        // If we didn't return, we didn't use an existing line.
        if (cantFitExtraLine)				// run out of room
            return false;
        
        // Still room: add a new line. The new line has the largest yPos (furthest down texture),
        // but the lines array must remain ordered by line height (lowest to heighest).
        Line line;
        line.yPos = nextYPos;
        line.height = attr.h * EXTRA_H;
        line.length = attr.w;
        size_t i = 0;
        while (i < lines.length && lines[i].height < line.height) ++i;
        lines = lines[0..i] ~ line ~ lines[i..$];	// keep lines sorted by height
        nextYPos += line.height;
        
        attr.x = 0;	// first glyph in the line
        attr.y = line.yPos;
        return true;
    }
    
    // Publically accessible data:
    uint texID;				// OpenGL texture identifier (for BindTexture)
    
private:
    const WASTE_H = 1.3;
    const EXTRA_H = 1;	// can be float/double, just experimenting with 1
    struct Line {
        int yPos;	// y position (xPos is always 0)
        int height;
        int length;
    }
    Line[] lines;
    int nextYPos = 0;	// y position for next created line (0 for first line)
}

struct fontOpts {
static:
    EnumContent mode;
    int modeFlag;
    /* lcdFilter should come from enum FT_LcdFilter:
    * FT_LCD_FILTER_NONE (0), FT_LCD_FILTER_DEFAULT (1), FT_LCD_FILTER_LIGHT (2) */
    EnumContent lcdFilter;
    IntContent defaultSize;
    StringContent defaultFont;
    
    static this() {
        mode = new EnumContent ("Font.mode", ["normal"[],"light","lcd","lcd_v","lcd_bgr","lcd_bgr_v"]);
        lcdFilter = new EnumContent ("Font.lcdFilter", ["none"[],"default","light"]);
        defaultSize = new IntContent ("Font.defaultSize");
        defaultFont = new StringContent ("Font.defaultFont");
        mode.addCallback (delegate void(IContent) {
           /* modeFlag should have one of the following values:
            * FT_LOAD_TARGET_NORMAL    (0x00000)
            * FT_LOAD_TARGET_LIGHT     (0x10000)
            * FT_LOAD_TARGET_LCD       (0x30000)
            * FT_LOAD_TARGET_LCD_V     (0x40000)
            * The mode FT_LOAD_TARGET_MONO (0x20000) is unsupported. */
            modeFlag = fontOpts.mode();
            if (modeFlag == 2 || modeFlag == 4) modeFlag = 0x30000;
            else if (modeFlag == 3 || modeFlag == 5) modeFlag = 0x40000;
            else modeFlag <<= 16;
        });
    }
}

struct GlyphAttribs {
    int x, y;	// position within texture
    int w, h;	// bitmap size
    
    int left, top;	// bitmap_left, bitmap_top fields
    int advanceX;	// horizontal advance distance
    uint index;		// glyph index (within face)
    
    uint texID;	// gl tex identifier
}

/** Cached information for drawing a block of text.
 *
 * Struct should be stored externally and updated via references. */
struct TextBlock {
    CharCache[] chars;	/// All chars. They hold x & y pos. info, so don't need to know about lines.
    int cacheVer = -1;	/// Checked on access; must equalFontTexture.cacheVer or the cache is rebuilt.
    int w, h;		/// Size of the block.
}
struct CharCache {
    GlyphAttribs* ga;	/// The character
    int xPos, yPos;	/// Character's x,y position
}