WIP: to use AGG font renderer to create a coverage bitmap

notes.md

@@ -0,0 +1,78 @@
+```c
+stbtt_InitFont
+
+stbtt_ScaleForMappingEmToPixels x 3
+stbtt_ScaleForPixelHeight
+stbtt_BakeFontBitmap
+stbtt_GetFontVMetrics x 2
+
+typedef struct {
+   unsigned short x0, y0, x1, y1; // coordinates of bbox in bitmap
+   float xoff, yoff, xadvance;
+} stbtt_bakedchar;
+
+struct RenImage {
+  RenColor *pixels;
+  int width, height;
+};
+
+typedef struct {
+  RenImage *image;
+  stbtt_bakedchar glyphs[256];
+} GlyphSet;
+
+struct RenFont {
+  void *data;
+  stbtt_fontinfo stbfont;
+  GlyphSet *sets[MAX_GLYPHSET];
+  float size;
+  int height;
+};
+
+```
+
+The function stbtt_BakeFontBitmap is used to write bitmap data into set->image->pixels (where set is a GlyphSet).
+Note that set->image->pixels need data in RGB format. After stbtt_BakeFontBitmap call the bitmap data are converted into RGB.
+With a single call many glyphs corresponding to a range of codepoints, all in a
+single image.
+
+## STB truetype font metrics
+
+stbtt_ScaleForPixelHeight takes a float 'height' and returns height / (ascent - descent).
+
+stbtt_ScaleForMappingEmToPixels take a float 'pixels' and returns pixels / unitsPerEm.
+
+### Computing RenFont
+
+When loading a font, in renderer.c, the font->height is determined as:
+
+```c
+int ascent, descent, linegap;
+stbtt_GetFontVMetrics(&font->stbfont, &ascent, &descent, &linegap);
+float scale = stbtt_ScaleForMappingEmToPixels(&font->stbfont, font->size);
+font->height = (ascent - descent + linegap) * scale + 0.5;
+```
+
+so, mathematically
+
+```c
+font->height = (ascent - descent + linegap) * font->size / unitsPerEm + 0.5;
+```
+
+**TO DO**: find out for what font->height is actually used.
+
+### Call to BakeFontBitmap
+
+In the same file, renderer.c, to create the glyphset image it computes:
+
+```c
+// Using stbtt functions
+float s = ScaleForMappingEmToPixels(1) / ScaleForPixelHeight(1);
+```
+
+so 's' is actually equal to (ascent - descent) / unitsPerEm.
+
+Then BakeFontBitmap is called and `font->size * s` is used for the pixel_height argument.
+So BakeFontBitmap gets, for pixel_height, (ascent - descent) * font->size / unitsPerEm.
+This is equal almost equal to font->height except the 0.5, the missing linegap calculation
+and the fact that this latter is an integer instead of a float.

notes.txt

@@ -1,34 +0,0 @@
-stbtt_InitFont
-
-stbtt_ScaleForMappingEmToPixels x 3
-stbtt_ScaleForPixelHeight
-stbtt_BakeFontBitmap
-stbtt_GetFontVMetrics x 2
-
-struct RenImage {
-  RenColor *pixels;
-  int width, height;
-};
-
-typedef struct {
-  RenImage *image;
-  stbtt_bakedchar glyphs[256];
-} GlyphSet;
-
-struct RenFont {
-  void *data;
-  stbtt_fontinfo stbfont;
-  GlyphSet *sets[MAX_GLYPHSET];
-  float size;
-  int height;
-};
-
-typedef struct {
-   unsigned short x0, y0, x1, y1; // coordinates of bbox in bitmap
-   float xoff, yoff, xadvance;
-} stbtt_bakedchar;
-
-The function stbtt_BakeFontBitmap is used to write bitmap data into set->image->pixels (where set is a GlyphSet).
-Note that set->image->pixels need data in RGB format. After stbtt_BakeFontBitmap call the bitmap data are converted into RGB.
-With a single call many glyphs corresponding to a range of codepoints, all in a
-single image.

src/font_render_capi.cpp

@@ -21,6 +21,7 @@ int FontRendererDrawText(FontRenderer *fr_, RenColor *pixels, int width, int hei
     font_renderer_lcd *font_renderer = (font_renderer_lcd *) fr_;
     agg::rendering_buffer ren_buf((agg::int8u *) pixels, width, height, -pitch);
     const agg::rgba8 agg_color(color.r, color.g, color.b);
-    double new_x = font_renderer->render_text(ren_buf, (double) text_size, agg_color, (double) x, (double) (height - y), text);
-    return int(new_x);
+    double xd = x, yd = (height - y - text_size);
+    font_renderer->render_text(ren_buf, (double) text_size, agg_color, xd, yd, text);
+    return int(xd);
 }

src/font_render_lcd.h

@@ -63,11 +63,11 @@ public:
     }
 
     template<class Rasterizer, class Scanline, class RenSolid>
-    double draw_text(Rasterizer& ras, Scanline& sl, 
-                     RenSolid& ren_solid, const agg::rgba8 color,
-                     const char* text,
-                     double x, double y, double height,
-                     unsigned subpixel_scale)
+    void draw_text(Rasterizer& ras, Scanline& sl, 
+                   RenSolid& ren_solid, const agg::rgba8 color,
+                   const char* text,
+                   double& x, double& y, double height,
+                   unsigned subpixel_scale)
     {
         const double scale_x = 100;
 
@@ -77,14 +77,14 @@ public:
 
         const char* p = text;
 
-        x *= subpixel_scale;
-        double start_x = x;
+        double x_lcd = x * subpixel_scale;
+        double start_x_lcd = x_lcd;
 
         while(*p)
         {
             if(*p == '\n')
             {
-                x = start_x;
+                x_lcd = start_x_lcd;
                 y -= height * 1.25;
                 ++p;
                 continue;
@@ -95,7 +95,7 @@ public:
             {
                 if(m_kerning)
                 {
-                    m_fman.add_kerning(&x, &y);
+                    m_fman.add_kerning(&x_lcd, &y);
                 }
 
                 m_fman.init_embedded_adaptors(glyph, 0, 0);
@@ -105,19 +105,20 @@ public:
                     ras.reset();
                     m_mtx.reset();
                     m_mtx *= agg::trans_affine_scaling(1.0 / scale_x, 1);
-                    m_mtx *= agg::trans_affine_translation(start_x + x/scale_x, ty);
+                    m_mtx *= agg::trans_affine_translation(start_x_lcd + x_lcd / scale_x, ty);
                     ras.add_path(m_trans);
                     ren_solid.color(color);
                     agg::render_scanlines(ras, sl, ren_solid);
                 }
 
                 // increment pen position
-                x += glyph->advance_x;
+                x_lcd += glyph->advance_x;
                 y += glyph->advance_y;
             }
             ++p;
         }
-        return x / (subpixel_scale * scale_x);
+        // Update x value befor returning.
+        x = x_lcd / subpixel_scale;
     }
 
     void clear(agg::rendering_buffer& ren_buf, const agg::rgba8 color) {
@@ -126,14 +127,14 @@ public:
         ren_base.clear(color);
     }
 
-    double render_text(agg::rendering_buffer& ren_buf,
+    void render_text(agg::rendering_buffer& ren_buf,
         const double text_size,
         const agg::rgba8 text_color,
         double x, double y,
         const char *text)
     {
         if (!m_font_loaded) {
-            return y;
+            return;
         }
 
         agg::scanline_u8 sl;
@@ -146,7 +147,7 @@ public:
             agg::pixfmt_bgra32 pf(ren_buf);
             base_ren_type ren_base(pf);
             renderer_solid ren_solid(ren_base);
-            y = draw_text(ras, sl, ren_solid, text_color, text, x, y, text_size, 1);
+            draw_text(ras, sl, ren_solid, text_color, text, x, y, text_size, 1);
         }
         else
         {
@@ -158,8 +159,7 @@ public:
             pixfmt_lcd_type pf_lcd(ren_buf, lut, m_gamma_lut);
             agg::renderer_base<pixfmt_lcd_type> ren_base_lcd(pf_lcd);
             agg::renderer_scanline_aa_solid<agg::renderer_base<pixfmt_lcd_type> > ren_solid_lcd(ren_base_lcd);
-            y = draw_text(ras, sl, ren_solid_lcd, text_color, text, x, y, text_size, 3);
+            draw_text(ras, sl, ren_solid_lcd, text_color, text, x, y, text_size, 3);
         }
-        return y;
     }
 };

tests/agg_font_render_test.cpp

@@ -0,0 +1,127 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#include "SDL_surface.h"
+#include "font_render_lcd.h"
+
+#define MAX_GLYPHSET 256
+
+typedef struct { uint8_t b, g, r, a; } RenColor;
+typedef struct { int x, y, width, height; } RenRect;
+
+struct RenImage {
+  RenColor *pixels;
+  int width, height;
+};
+
+struct GlyphSetA {
+  RenImage *image;
+  // FIXME: add glyphs information for AGG implementation
+  // stbtt_bakedchar glyphs[256];
+};
+
+struct RenFontA {
+  font_renderer_lcd *renderer;
+  float size;
+  int height;
+};
+
+static void* check_alloc(void *ptr) {
+  if (!ptr) {
+    fprintf(stderr, "Fatal error: memory allocation failed\n");
+    exit(EXIT_FAILURE);
+  }
+  return ptr;
+}
+
+RenImage* ren_new_image(int width, int height) {
+  assert(width > 0 && height > 0);
+  RenImage *image = malloc(sizeof(RenImage) + width * height * sizeof(RenColor));
+  check_alloc(image);
+  image->pixels = (void*) (image + 1);
+  image->width = width;
+  image->height = height;
+  return image;
+}
+
+void ren_free_image(RenImage *image) {
+  free(image);
+}
+
+RenFontA* ren_load_font_agg(const char *filename, float size) {
+  RenFont *font = NULL;
+
+  /* init font */
+  font = check_alloc(calloc(1, sizeof(RenFontA)));
+  font->size = size;
+
+  font->renderer = new font_renderer_lcd(true, false, true, 1.8);
+  font->renderer->load_font(filename);
+
+  // FIXME: figure out correct calculation for font->height with
+  // ascent, descent and linegap.
+  fit->height = size;
+  return font;
+}
+
+static GlyphSet* load_glyphset_agg(RenFont *font, int idx) {
+  GlyphSet *set = check_alloc(calloc(1, sizeof(GlyphSet)));
+
+  /* init image */
+  int width = 128;
+  int height = 128;
+retry:
+  set->image = ren_new_image(width, height);
+
+  /* load glyphs */
+  float s =
+    stbtt_ScaleForMappingEmToPixels(&font->stbfont, 1) /
+    stbtt_ScaleForPixelHeight(&font->stbfont, 1);
+  int res = stbtt_BakeFontBitmap(
+    font->data, 0, font->size * s, (void*) set->image->pixels,
+    width, height, idx * 256, 256, set->glyphs);
+
+  /* retry with a larger image buffer if the buffer wasn't large enough */
+  if (res < 0) {
+    width *= 2;
+    height *= 2;
+    ren_free_image(set->image);
+    goto retry;
+  }
+
+  /* adjust glyph yoffsets and xadvance */
+  int ascent, descent, linegap;
+  stbtt_GetFontVMetrics(&font->stbfont, &ascent, &descent, &linegap);
+  float scale = stbtt_ScaleForMappingEmToPixels(&font->stbfont, font->size);
+  int scaled_ascent = ascent * scale + 0.5;
+  for (int i = 0; i < 256; i++) {
+    set->glyphs[i].yoff += scaled_ascent;
+    set->glyphs[i].xadvance = floor(set->glyphs[i].xadvance);
+  }
+
+  /* convert 8bit data to 32bit */
+  for (int i = width * height - 1; i >= 0; i--) {
+    uint8_t n = *((uint8_t*) set->image->pixels + i);
+    set->image->pixels[i] = (RenColor) { .r = 255, .g = 255, .b = 255, .a = n };
+  }
+
+  return set;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc < 3) {
+        fprintf(stderr, "usage: %s <font-filename> <size>\n", argv[0]);
+        return 1;
+    }
+    const char *filename = argv[1];
+    const int size = atoi(argv[2]);
+    RenFont *font = ren_load_font(filename, size);
+    GlyphSet *set = load_glyphset(font, 0);
+    SDL_Surface *surface = SDL_CreateRGBSurfaceWithFormatFrom(
+        set->image->pixels,
+        set->image->width, set->image->height, 32, set->image->width * 4,
+        SDL_PIXELFORMAT_RGBA32);
+    SDL_SaveBMP(surface, "stb-glyphset.bmp");
+    return 0;
+}