vn/code/vn_font.cpp

#define GLYPH_SUBPIXEL_SEGMENTS 3

global read_only s32 Font_Oversample = 2;

inline s32 GetSubpixelSegmentAtP(r32 Value)
{
	s32 Result = (s32)(Value - Floor(Value))*GLYPH_SUBPIXEL_SEGMENTS;
	return(Result);
}

static void RasterizeGlyph(glyph_atlas *Atlas, font_id Font, glyph *Glyph, u32 Codepoint, r32 Size, s32 Subpixel)
{
	Glyph->Font = Font;
	Glyph->Codepoint = Codepoint;
	Glyph->Size = Size;
	Glyph->Subpixel = Subpixel;
	
	Assert(Subpixel < GLYPH_SUBPIXEL_SEGMENTS);
	
	loaded_font *LoadedFont = Atlas->Fonts + Font;
	stbtt_fontinfo *Info = &LoadedFont->Info;
	
	r32 Scale = stbtt_ScaleForMappingEmToPixels(Info, Size);
	
	s32 InternalIndex = (s32)(Glyph - Atlas->Glyphs);
	s32 GlyphsPerRow = Atlas->BitmapSize / Atlas->GlyphSize;
	
	v2_s32 BaseTextureOffset = V2S32((InternalIndex % GlyphsPerRow)*Atlas->GlyphSize,
                                     (InternalIndex / GlyphsPerRow)*Atlas->GlyphSize);
	
	int GlyphIndex = stbtt_FindGlyphIndex(Info, Codepoint);
	
	stbtt_GetGlyphBitmapBoxSubpixel(Info, GlyphIndex, Scale, Scale,
                                    (r32)Subpixel/GLYPH_SUBPIXEL_SEGMENTS, 0,
                                    &Glyph->P0.x, &Glyph->P0.y, &Glyph->P1.x, &Glyph->P1.y);
	
	Fill(Atlas->BitmapBuffer, 0, Atlas->GlyphSize*Atlas->GlyphSize);
	stbtt_MakeGlyphBitmapSubpixel(Info, Atlas->BitmapBuffer,
                                  Atlas->GlyphSize, Atlas->GlyphSize, Atlas->GlyphSize,
                                  Scale, Scale,
                                  (r32)Subpixel/GLYPH_SUBPIXEL_SEGMENTS, 0,
                                  GlyphIndex);
	
	s32 Advance, LeftSideBearing;
	stbtt_GetGlyphHMetrics(Info, GlyphIndex, &Advance, &LeftSideBearing);
	Glyph->Advance = Advance*Scale;
	Glyph->Offset.x = LeftSideBearing*Scale;
	
	Glyph->Offset.y = Glyph->P0.y + (LoadedFont->Ascent + LoadedFont->LineGap)*Scale;
	
	v2_s32 Dim = Glyph->P1 - Glyph->P0;
	
	Glyph->P0 = BaseTextureOffset;
	Glyph->P1 = BaseTextureOffset + Dim + V2S32(2, 2);
	
	Atlas->RenderCommands->FillRegion(Atlas->Texture,
                                      BaseTextureOffset, V2S32(Atlas->GlyphSize, Atlas->GlyphSize),
                                      Atlas->BitmapBuffer);
}

static glyph *GetGlyph(glyph_atlas *Atlas, font_id Font, u32 Codepoint, r32 Size, s32 Subpixel)
{
	glyph *Glyph = 0;
	
	for(s32 GlyphIndex = 0;
        GlyphIndex < Atlas->GlyphsUsed;
        ++GlyphIndex)
	{
		glyph *At = Atlas->Glyphs + GlyphIndex;
		if((At->Font == Font) && (At->Codepoint == Codepoint) && (At->Size == Size) && (At->Subpixel == Subpixel))
		{
			Glyph = At;
			break;
		}
	}
	
	if(Glyph)
	{
		DLLRemove_NP(Atlas->LRUFirst, Atlas->LRULast, Glyph, LRUNext, LRUPrev);
	}
	else
	{
		if(Atlas->GlyphsUsed < Atlas->MaxGlyphCount)
		{
			Glyph = Atlas->Glyphs + Atlas->GlyphsUsed++;
		}
		else
		{
			Glyph = Atlas->LRUFirst;
			Assert(Glyph);
			
			DLLRemove_NP(Atlas->LRUFirst, Atlas->LRULast, Glyph, LRUNext, LRUPrev);
		}
		
		RasterizeGlyph(Atlas, Font, Glyph, Codepoint, Size, Subpixel);
	}
	
	DLLInsertLast_NP(Atlas->LRUFirst, Atlas->LRULast, Glyph, LRUNext, LRUPrev);
	
	return(Glyph);
}

static glyph_atlas *CreateGlyphAtlas(vn_render_commands *RenderCommands,
                                     s32 BitmapSize = DEFAULT_GLYPH_ATLAS_DIM,
                                     s32 GlyphSize = MAX_GLYPH_SIZE)
{
	arena *Arena = ArenaAlloc(Megabytes(1), true);
	glyph_atlas *Atlas = PushStruct(Arena, glyph_atlas);
	Atlas->Arena = Arena;
	
	Atlas->BitmapSize = BitmapSize;
	Atlas->GlyphSize = GlyphSize;
	
	Atlas->MaxGlyphCount = (DEFAULT_GLYPH_ATLAS_DIM / MAX_GLYPH_SIZE)*(DEFAULT_GLYPH_ATLAS_DIM / MAX_GLYPH_SIZE);
	Atlas->Glyphs = PushArray(Atlas->Arena, glyph, Atlas->MaxGlyphCount);
	
	Atlas->RenderCommands = RenderCommands;
	Atlas->Texture = RenderCommands->AllocateTexture(V2S32(BitmapSize, BitmapSize), Render_TextureFormat_R8, false, 0);
	
	Atlas->Fonts[Font_Regular].Data          = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/Roboto-Regular.ttf"));
	Atlas->Fonts[Font_Bold].Data             = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/Roboto-Bold.ttf"));
	Atlas->Fonts[Font_Monospace].Data        = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/DejaVuSansMono.ttf"));
	Atlas->Fonts[Font_MonospaceOblique].Data = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/DejaVuSansMono-Oblique.ttf"));
	Atlas->Fonts[Font_Fancy].Data            = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/Merriweather-Regular.ttf"));
	Atlas->Fonts[Font_Icons].Data            = Platform_ReadEntireFile(Atlas->Arena, StrLit("data/fonts/icons.ttf"));
	
	for(s32 FontIndex = 0;
        FontIndex < Font_Count;
        ++FontIndex)
	{
		loaded_font *Font = Atlas->Fonts + FontIndex;
		stbtt_InitFont(&Font->Info,
                       Font->Data.Data,
                       stbtt_GetFontOffsetForIndex(Font->Data.Data, 0));
		
		stbtt_GetFontVMetrics(&Font->Info, &Font->Ascent, &Font->Descent, &Font->LineGap);
	}
	
	Atlas->BitmapBuffer = PushArray(Atlas->Arena, u8, GlyphSize*GlyphSize);
	
	return(Atlas);
}

static r32 PushText(render_group *Group, glyph_atlas *Atlas, font_id Font,
                    v2 P, r32 Size, v4 Color,
                    string Text)
{
	r32 OffsetX = 0;
	u8 *TextBegin = Text.Data;
	u8 *TextEnd = TextBegin+Text.Count;
	for(u8 *Byte = TextBegin; Byte < TextEnd;)
	{
		string_decode Decode = DecodeUTF8Codepoint(Byte, TextEnd-Byte);
		Byte += Decode.Size;
		u32 Codepoint = Decode.Codepoint;
		
		glyph *Glyph = GetGlyph(Atlas, Font, Codepoint, Size*Font_Oversample, GetSubpixelSegmentAtP(P.x*Font_Oversample));
		Assert(Glyph);
		
		v2 GlyphP = P + Glyph->Offset*(1.0 / Font_Oversample) + V2(OffsetX, 1);
		
		v2 RenderDim = ConvertV2ToR32(Glyph->P1 - Glyph->P0);
		v2 Dim = RenderDim*(1.0 / Font_Oversample);
		
		PushTexturedQuad(Group,
                         Range2R32(GlyphP, GlyphP+Dim),
                         Range2R32(ConvertV2ToR32(Glyph->P0), ConvertV2ToR32(Glyph->P1)),
                         Color, Color, Color, Color, 0, 0, 0, Atlas->Texture);
		
		OffsetX += Glyph->Advance/Font_Oversample;
	}
	return(OffsetX);
}

static void PushTextF(render_group *Group, glyph_atlas *Atlas, font_id Font,
                      v2 P, r32 Size, v4 Color,
                      char *Format, ...)
{
	temp Scratch = GetScratch(0, 0);
	
	va_list Arguments;
	va_start(Arguments, Format);
	string String = PushFormatVariadic(Scratch.Arena, Format, Arguments);
	va_end(Arguments);
	
	PushText(Group, Atlas, Font, P, Size, Color, String);
	
	ReleaseScratch(Scratch);
}

inline r32 CalculateRasterizedTextWidth(glyph_atlas *Atlas, font_id Font, r32 Size, string Text)
{
	r32 X = 0;
	
	u8 *TextBegin = Text.Data;
	u8 *TextEnd = TextBegin+Text.Count;
	for(u8 *Byte = TextBegin; Byte < TextEnd;)
	{
		string_decode Decode = DecodeUTF8Codepoint(Byte, TextEnd-Byte);
		Byte += Decode.Size;
		u32 Codepoint = Decode.Codepoint;
		
		glyph *Glyph = GetGlyph(Atlas, Font, Codepoint, Size*Font_Oversample, GetSubpixelSegmentAtP(X*Font_Oversample));
		Assert(Glyph);
		
		X += Glyph->Advance/Font_Oversample;
	}
	
	return(X);
}

inline r32 CalculateRasterizedTextHeight(glyph_atlas *Atlas, font_id Font, r32 Size, string Text)
{
	r32 Scale = stbtt_ScaleForMappingEmToPixels(&Atlas->Fonts[Font].Info, Size)/
		stbtt_ScaleForPixelHeight(&Atlas->Fonts[Font].Info, Size);
	
	r32 Y = Size*Scale;
	
	u8 *TextBegin = Text.Data;
	u8 *TextEnd = TextBegin+Text.Count;
	for(u8 *Byte = TextBegin; Byte < TextEnd;)
	{
		string_decode Decode = DecodeUTF8Codepoint(Byte, TextEnd-Byte);
		Byte += Decode.Size;
		u32 Codepoint = Decode.Codepoint;
		
		if(Codepoint == '\n')
		{
			Y += Size*Scale;
		}
	}
	return(Y);
}