Adding basic font rendering functions:HEADmain

- moving existing code into separate function calls to make it easier

1 files changed, 143 insertions, 13 deletions

diff --git a/code/amr_fonts.h b/code/amr_fonts.h
index f44893c..81666a0 100644
--- a/code/amr_fonts.h
+++ b/code/amr_fonts.h
@@ -1,25 +1,46 @@
 #ifndef AMR_FONTS_H
 #define AMR_FONTS_H
 
-typedef struct amr_glyph_info {
-  u32 charset_start_index;
-  u32 charset_end_index;
-} amr_glyph_info;
+#define LATIN_BASIC_START_INDEX 32
+#define LATIN_BASIC_END_INDEX 126
 
-typedef struct amr_font_details_debug {
+typedef struct amr_letter_details_debug {
   i32 advance;
   i32 lsb;
   i32 x0, y0, x1, y1;
-  i32 kern;
-  f32 lx;
-  f32 ly;
   i32 byte_offset;
-  i32 baseline;
-} debug_font_details;
+  // @TODO: check if offsets are in PX
+  f32 StartingYOffset;
+  f32 StartingXOffset;
+} amr_letter_details_debug;
 
 typedef struct amr_font_state_debug {
   stbtt_fontinfo font_info;
+  amr_letter_details_debug font_details;
+  // font metrics
+  f32 font_size;
+  f32 scale_factor;
+  i32 ascent;
+  i32 descent;
+  i32 line_gap;
+  // glyphs
+  u32 charset_start_index;
+  u32 charset_end_index;
+  
+  // @TODO: make this array
+  u32 *glyph_index_array;
+  u32 glyph_count;
+
+  // text specific metrics
+  // @TODO: these should probably be moved to an array or remain out of this struct
+  f32 Baseline;
+  f32 MaxLineWidthPx;
+  // font bitmap info
+  unsigned char *FontBitmap;
+  u32 FontBitmapWidth;
+  u32 FontBitmapHeight;
 } amr_font_state;
+
 // initialise a font and loads the font in the fontbuffer
 // input: 
 // - font path
@@ -28,7 +49,16 @@ typedef struct amr_font_state_debug {
 // output:
 // - error code
 u32 amr_InitFont(const u8 *FontPath, u8 *FontBuffer, u32 FontFz); 
-u32 amr_GetGlyphIdFromCodepoint(amr_glyph_info glyph, u32 *GlyphIndexArray, u32 Codepoint);
+void amr_LoadFontMetrics(amr_font_state font, u32 FontSize);
+void amr_LoadGlyphsFromFont(amr_DebugArena *MemoryArena, amr_font_state *font);
+u32 amr_GetGlyphIdFromCodepoint(amr_font_state font, u32 Codepoint);
+
+//////////////////////////////////////////////////////////////////////////////
+/// Naive Font Bitmap generation
+/// This approach is fast but usese more memory
+/// We make a single draw call, but load the entire text in a single bitmap
+//////////////////////////////////////////////////////////////////////////////
+void amr_MakeFontBitmapNaive(GameState *State, amr_font_state *Font, char *Text, u32 TextSize);
 
 u32 amr_InitFont(stbtt_fontinfo *font_info, const char *FontPath, u8 *FontBuffer, u32 FontSz)
 {
@@ -42,10 +72,110 @@ u32 amr_InitFont(stbtt_fontinfo *font_info, const char *FontPath, u8 *FontBuffer
   return 0;
 }
 
-u32 amr_GetGlyphIdFromCodepoint(amr_glyph_info glyph, u32 *GlyphIndexArray, u32 Codepoint)
+void amr_LoadFontMetrics(amr_font_state *Font, f32 FontSize)
+{
+    // get a SF (scale factor)
+    Font->scale_factor = stbtt_ScaleForPixelHeight(&(Font->font_info), FontSize);
+
+    // get vertical metrics
+    stbtt_GetFontVMetrics(&(Font->font_info), &(Font->ascent),
+        &(Font->descent), &(Font->line_gap));
+}
+
+void amr_LoadGlyphsFromFont(amr_DebugArena *MemoryArena, amr_font_state *Font)
+{
+    Font->glyph_count = Font->charset_end_index - Font->charset_start_index;
+    Font->glyph_index_array = (u32 *)amr_ArenaAlloc(MemoryArena, 
+        sizeof(Font->glyph_count) * Font->glyph_count);
+
+    u32 *array_iter = Font->glyph_index_array;
+    for (u32 i = 0; i < Font->glyph_count; i++)
+    {
+      u32 offset_codepoint = Font->charset_start_index + i;
+      *array_iter = stbtt_FindGlyphIndex(&(Font->font_info), offset_codepoint);
+      array_iter++;
+    }
+}
+
+u32 amr_GetGlyphIdFromCodepoint(amr_font_state Font, u32 Codepoint)
 {
-  u32 glyph_id = *(GlyphIndexArray + (Codepoint - glyph.charset_start_index));
+  u32 glyph_id = *(Font.glyph_index_array + (Codepoint - Font.charset_start_index));
   return glyph_id;
 }
 
+void amr_MakeFontBitmapNaive(GameState *State, amr_font_state *Font, char *Text, u32 TextSize)
+{
+  Font->MaxLineWidthPx = 0.0f;
+  Font->Baseline = roundf(Font->ascent * Font->scale_factor);
+
+  u32 fd_sz = sizeof(amr_letter_details_debug)*TextSize;
+  amr_letter_details_debug *fd_arr = (amr_letter_details_debug *)amr_ArenaAlloc(&(State->Memory.Arena), fd_sz);
+  amr_letter_details_debug *_fi = fd_arr;
+
+  f32 RunningXOffset = 0.0f;
+  // convert str to font
+  for (i32 i = 0; i < TextSize; ++i)
+  {
+    _fi->StartingXOffset = RunningXOffset;
+    if (Text[i] == '\n')
+    {
+      // if new line, move baseline down
+      Font->Baseline += (i32)roundf((Font->ascent - Font->descent
+            + Font->line_gap) * Font->scale_factor);
+      RunningXOffset = 0;
+      ++_fi;
+      continue;
+    }
+
+    u32 GlyphId = amr_GetGlyphIdFromCodepoint(*Font, Text[i]);
+    stbtt_GetGlyphHMetrics(&(Font->font_info), GlyphId,
+        &_fi->advance, &_fi->lsb);
+    stbtt_GetGlyphBitmapBox(&(Font->font_info), GlyphId,
+        Font->scale_factor, Font->scale_factor, 
+        &_fi->x0, &_fi->y0, &_fi->x1, &_fi->y1);
+
+    _fi->StartingYOffset = (f32)(Font->Baseline + _fi->y0);
+    RunningXOffset += (_fi->advance * Font->scale_factor);
+    
+    if (i < TextSize - 1 && Text[i+1] != '\n')
+    {
+      i32 kern = stbtt_GetGlyphKernAdvance(&(Font->font_info), 
+          GlyphId, amr_GetGlyphIdFromCodepoint(*Font, Text[i+1]));
+      RunningXOffset += roundf(kern * Font->scale_factor);
+    }
+
+    if (RunningXOffset > Font->MaxLineWidthPx)
+    {
+      Font->MaxLineWidthPx = RunningXOffset;
+    }
+    ++_fi;
+  }
+
+  // make all the glyphs into bitmaps. 
+  _fi = fd_arr;
+  Font->FontBitmapWidth = (u32)Font->MaxLineWidthPx;
+  Font->FontBitmapHeight = (u32)(Font->Baseline - 
+      roundf(Font->scale_factor * Font->descent));
+  
+  u32 bitmap_size = sizeof(unsigned char)*Font->FontBitmapWidth*Font->FontBitmapHeight;
+  Font->FontBitmap = (unsigned char *)amr_ArenaAlloc(&(State->Memory.Arena), bitmap_size);
+
+  _fi = fd_arr;
+  for (int i = 0; i < TextSize; i++)
+  {
+    if (Text[i] == '\n') {
+      ++_fi;
+      continue;
+    }
+    _fi->byte_offset = (i32)(_fi->StartingXOffset + roundf(_fi->lsb * Font->scale_factor) + 
+        (_fi->StartingYOffset * Font->FontBitmapWidth)) ;
+    // store image data in bitmap
+    stbtt_MakeGlyphBitmap(&(Font->font_info), Font->FontBitmap + _fi->byte_offset, 
+        _fi->x1 - _fi->x0, _fi->y1 - _fi->y0, Font->FontBitmapWidth, 
+        Font->scale_factor, Font->scale_factor, 
+        amr_GetGlyphIdFromCodepoint(*Font, Text[i]));
+    _fi++;
+  }
+}
+
 #endif