dlib/fonts.d

module dlib.fonts;

import dlibincludes;
import dlib.aliases;
import dlib.util;
import dlib.alloc;
import dlib.math;
import std.math.traits : isNaN;

struct FontAtlas
{
	Glyph[128]  glyphs;
	FontMetrics metrics;
	u32         size;
	UVec2       dimensions;

	alias metrics this;
}

struct FontMetrics
{
	f32 ascent;
	f32 descent;
	f32 line_gap;
	f32 line_height;
	f32 max_advance;
}

struct Glyph
{
	dchar ch;
	f32		advance;
	f32		plane_left;
	f32		plane_bottom;
	f32 	plane_right;
	f32 	plane_top;
	f32		atlas_left;
	f32 	atlas_bottom;
	f32		atlas_right;
	f32		atlas_top;
}

__gshared FT_Library FT_LIB;
alias     FontFace = FT_Face;

struct FontAtlasBuf
{
	u8[] 	data;
	FontAtlas atlas;
}

shared static this()
{
	FT_Init_FreeType(&FT_LIB);
}

void
CloseFreeType()
{
	if(FT_LIB)
	{
		FT_Done_FreeType(FT_LIB);
	}
}

FontFace
OpenFont(u8[] data)
{
	FontFace font;
	FT_New_Memory_Face(FT_LIB, data.ptr, cast(FT_Long)data.length, 0, &font);
	return font;
}

void
CloseFont(FontFace font)
{
	if(font != null)
	{
		FT_Done_Face(font);
	}
}

i32
Float26(f32 f)
{
	return cast(i32)round(cast(f32)(1 << 6) * f);
}

u8
DeMultiply(u8 color, u8 alpha)
{
	u32 v = cast(u32)(255.0 * cast(f32)(color) / cast(f32)(alpha + f32.epsilon) + 0.5);
	return v > 255 ? 255 : cast(u8)v;
}

u32
TextSize(f32 s)
{
	return cast(u32)((96.0f/72.0f) * s);
}

FontAtlasBuf
CreateAtlas(Arena* arena, FontFace font, u32 size, UVec2 atlas_dim)
{
	FontAtlasBuf abuf = {
		data: Alloc!(u8)(arena, atlas_dim.x * atlas_dim.y * 4),
		atlas: {
			size:       size,
			dimensions: atlas_dim,
		},
	};

	// TODO: proper packing algorithm
	if(font != null)
	{
		FT_Set_Pixel_Sizes(font, 0, TextSize(size));

		i64 bbox_ymax = font.bbox.yMax >> 6;
		i64 bbox_ymin = font.bbox.yMin >> 6;

		u64 baseline    = font.size.metrics.ascender >> 6;
		u64 line_height = (font.size.metrics.height >> 6)+1;

		abuf.atlas.line_height = line_height;
		abuf.atlas.max_advance = font.size.metrics.max_advance >> 6;

		u32 max_w, max_h, count;

		i32 font_size = Float26(size);

		const u32 PADDING = 2;
		foreach(FT_ULong char_code; 0 .. 0x7F)
		{
			FT_Error res = FT_Load_Char(font, char_code, cast(FT_Int32)FT_LOAD_RENDER);
			if(res != 0)
			{
				continue;
			}

			u32 bmp_w = font.glyph.bitmap.width;
			u32 bmp_h = font.glyph.bitmap.rows;
			if(max_w + bmp_w > atlas_dim.x)
			{
				max_h += line_height+PADDING;
				max_w  = 0;
			}

			if(max_h > atlas_dim.y)
			{
				Logf("Unable to pack atlas within dimensions provided");
				assert(false);
			}
			
			max_w    += bmp_w;
			count    += 1;
		}

		max_w = max_h = count = 0;

		foreach(FT_ULong char_code; 0 .. 0x7F)
		{
			FT_Error res = FT_Load_Char(font, char_code, cast(FT_Int32)FT_LOAD_RENDER);
			if(res != 0)
			{
				continue;
			}

			FT_GlyphSlot glyph = font.glyph;
			FT_Bitmap*   bmp   = &font.glyph.bitmap;

			if(max_w + bmp.rows > atlas_dim.x)
			{
				max_h += line_height+PADDING;
				max_w  = PADDING;
			}

			i64 base = Max(baseline, font.glyph.bitmap_top);

			switch(bmp.pixel_mode)
			{
				case FT_PIXEL_MODE_BGRA:
					{
						u64 x, y;
						foreach(r; 0 .. bmp.rows)
						{
							y = (base - font.glyph.bitmap_top + r) + max_h;
							foreach(c; 0 .. bmp.width)
							{
								x = max_w + c;
								u64 offset = (y*atlas_dim.y + x) * 4;

								u8 p_b = bmp.buffer[offset+0];
								u8 p_g = bmp.buffer[offset+1];
								u8 p_r = bmp.buffer[offset+2];
								u8 p_a = bmp.buffer[offset+3];

								abuf.data[offset .. offset+4] = [DeMultiply(p_r, p_a), DeMultiply(p_b, p_a), DeMultiply(p_g, p_a), p_a];
							}
						}
					} break;
				case FT_PIXEL_MODE_MONO:
					{
						u32 pitch = bmp.pitch;
						u8* buf   = bmp.buffer;
					 	u64 x, y;
						foreach(r; 0 .. bmp.rows)
						{
							u8 bits = 0;
							u8* buf_ptr = buf;
							y = (base - font.glyph.bitmap_top + r) + max_h;
							foreach(c; 0 .. bmp.width)
							{
								if((c & 7) == 0)
								{
									bits = *buf_ptr;
									buf_ptr += 1;
								}

								x = max_w + c;
								u64 offset = (y*atlas_dim.y + x) * 4;

								abuf.data[offset .. offset+4] = [255, 255, 255, bits & 0x80 ? 255 : 0];
								bits <<= 1;
							}

							buf += pitch;
						}
					} break;
				case FT_PIXEL_MODE_GRAY:
					{
						u64 x, y;
						foreach(r; 0 .. bmp.rows)
						{
							y = (base - font.glyph.bitmap_top + r) + max_h;
							foreach(c; 0 .. bmp.width)
							{
								x = max_w + c;
								u64 offset = (y*atlas_dim.y + x) * 4;

								abuf.data[offset .. offset+4] = [255, 255, 255, bmp.buffer[r*bmp.pitch + c]];
							}
						}
					} break;
				default:
					assert(false, "Unknown pixel_mode value");
					break;
			}

			Glyph* g = abuf.atlas.glyphs.ptr + char_code;

			f32 height = glyph.metrics.height >> 6;
			f32 width  = glyph.metrics.width  >> 6;
			f32 top    = font.glyph.bitmap_top;
			f32 left   = font.glyph.bitmap_left;

			g.ch           = cast(dchar)char_code;
			g.advance      = cast(f32)(glyph.advance.x >> 6);
			g.plane_left   = left;
			g.plane_right  = g.plane_left + bmp.width;
			g.plane_top    = 0.0;
			g.plane_bottom = line_height;

			g.atlas_top    = max_h;
			g.atlas_left   = max_w;
			g.atlas_bottom = max_h + line_height;
			g.atlas_right  = max_w + bmp.width;

			max_w += bmp.width + PADDING;

			count += 1;
		}
	}

	return abuf;
}