allow font ranges with first_char = 0;

fix divide by 0 for exactly-vertical edges;
fix possible divide by 0 for exactly-horizontal edges
add documentation for stbtt_Rasterize;

stb_truetype.h

@@ -41,13 +41,14 @@
 //       Peter LaValle
 //       Sergey Popov
 //       Giumo X. Clanjor
+//       Higor Euripedes
 //
 //   Misc other:
 //       Ryan Gordon
 //
 // VERSION HISTORY
 //
-//   1.08 (2015-09-13) document stbtt_Rasterize()
+//   1.08 (2015-09-13) document stbtt_Rasterize(); fixes for vertical & horizontal edges
 //   1.07 (2015-08-01) allow PackFontRanges to accept arrays of sparse codepoints;
 //                     variant PackFontRanges to pack and render in separate phases;
 //                     fix stbtt_GetFontOFfsetForIndex (never worked for non-0 input?);
@@ -1695,7 +1696,7 @@ static stbtt__active_edge *stbtt__new_active(stbtt__hheap *hh, stbtt__edge *e, i
    //STBTT_assert(e->y0 <= start_point);
    if (!z) return z;
    z->fdx = dxdy;
-   z->fdy = (1/dxdy);
+   z->fdy = dxdy != 0.0f ? (1.0f/dxdy) : 0.0f;
    z->fx = e->x0 + dxdy * (start_point - e->y0);
    z->fx -= off_x;
    z->direction = e->invert ? 1.0f : -1.0f;
@@ -2098,11 +2099,13 @@ static void stbtt__rasterize_sorted_edges(stbtt__bitmap *result, stbtt__edge *e,
 
       // insert all edges that start before the bottom of this scanline
       while (e->y0 <= scan_y_bottom) {
-         stbtt__active_edge *z = stbtt__new_active(&hh, e, off_x, scan_y_top, userdata);
-         STBTT_assert(z->ey >= scan_y_top);
-         // insert at front
-         z->next = active;
-         active = z;
+         if (e->y0 != e->y1) {
+            stbtt__active_edge *z = stbtt__new_active(&hh, e, off_x, scan_y_top, userdata);
+            STBTT_assert(z->ey >= scan_y_top);
+            // insert at front
+            z->next = active;
+            active = z;
+         }
          ++e;
       }
 
@@ -2845,7 +2848,7 @@ STBTT_DEF int stbtt_PackFontRangesGatherRects(stbtt_pack_context *spc, stbtt_fon
       ranges[i].v_oversample = (unsigned char) spc->v_oversample;
       for (j=0; j < ranges[i].num_chars; ++j) {
          int x0,y0,x1,y1;
-         int codepoint = ranges[i].first_unicode_codepoint_in_range ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];
+         int codepoint = ranges[i].array_of_unicode_codepoints == NULL ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];
          int glyph = stbtt_FindGlyphIndex(info, codepoint);
          stbtt_GetGlyphBitmapBoxSubpixel(info,glyph,
                                          scale * spc->h_oversample,
@@ -2886,7 +2889,7 @@ STBTT_DEF int stbtt_PackFontRangesRenderIntoRects(stbtt_pack_context *spc, stbtt
          if (r->was_packed) {
             stbtt_packedchar *bc = &ranges[i].chardata_for_range[j];
             int advance, lsb, x0,y0,x1,y1;
-            int codepoint = ranges[i].first_unicode_codepoint_in_range ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];
+            int codepoint = ranges[i].array_of_unicode_codepoints == NULL ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];
             int glyph = stbtt_FindGlyphIndex(info, codepoint);
             stbrp_coord pad = (stbrp_coord) spc->padding;
 
@@ -3189,6 +3192,7 @@ STBTT_DEF int stbtt_FindMatchingFont(const unsigned char *font_collection, const
 
 // FULL VERSION HISTORY
 //
+//   1.08 (2015-09-13) document stbtt_Rasterize(); fixes for vertical & horizontal edges
 //   1.07 (2015-08-01) allow PackFontRanges to accept arrays of sparse codepoints;
 //                     allow PackFontRanges to pack and render in separate phases;
 //                     fix stbtt_GetFontOFfsetForIndex (never worked for non-0 input?);

tests/test_truetype.c

@@ -24,6 +24,7 @@ void debug(void)
 unsigned char temp_bitmap[BITMAP_H][BITMAP_W];
 stbtt_bakedchar cdata[256*2]; // ASCII 32..126 is 95 glyphs
 stbtt_packedchar pdata[256*2];
+
 int main(int argc, char **argv)
 {
    stbtt_fontinfo font;
@@ -35,6 +36,17 @@ int main(int argc, char **argv)
    // @TODO: why is minglui.ttc failing? 
    fread(ttf_buffer, 1, 1<<25, fopen(argc > 3 ? argv[3] : "c:/windows/fonts/mingliu.ttc", "rb"));
 
+   //fread(ttf_buffer, 1, 1<<25, fopen(argc > 3 ? argv[3] : "c:/x/DroidSansMono.ttf", "rb"));
+   {
+      static stbtt_pack_context pc;
+      static stbtt_packedchar cd[256];
+      static unsigned char atlas[1024*1024];
+
+      stbtt_PackBegin(&pc, atlas, 1024,1024,1024,1,NULL);
+      stbtt_PackFontRange(&pc, ttf_buffer, 0, 32.0, 0, 256, cd);
+      stbtt_PackEnd(&pc);
+   }
+
 #if 0
    stbtt_BakeFontBitmap(ttf_buffer,stbtt_GetFontOffsetForIndex(ttf_buffer,0), 40.0, temp_bitmap[0],BITMAP_W,BITMAP_H, 32,96, cdata); // no guarantee this fits!
    stbi_write_png("fonttest1.png", BITMAP_W, BITMAP_H, 1, temp_bitmap, 0);