[PATCH 4/5] font: Add font scaling feature to grub_font_draw_glyph()

[Zhang Boyang <zhangboyang.id@gmail.com>]

This patch adds an argument 'scale' to grub_font_draw_glyph(). If
scale > 1, then the function will create a new scaled bitmap of the
drawing glyph, and draws the scaled glyph. The scaled bitmap is cached
in the glyph itself, so it can be reused if same glyph is used many
times.

This patch also adds a new metadata entry named MAXS to font files,
limiting the maximum acceptable scale factor at runtime for a specific
font. Currently MAXS is set to 8, which is sufficient for 16K monitors.

Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
---
 grub-core/commands/videotest.c |  4 +-
 grub-core/font/font.c          | 91 +++++++++++++++++++++++++++++++---
 grub-core/gfxmenu/font.c       |  2 +-
 grub-core/term/gfxterm.c       |  2 +-
 include/grub/font.h            |  9 +++-
 5 files changed, 97 insertions(+), 11 deletions(-)

diff --git a/grub-core/commands/videotest.c b/grub-core/commands/videotest.c
index ac145afc2..d95ee411d 100644
--- a/grub-core/commands/videotest.c
+++ b/grub-core/commands/videotest.c
@@ -87,7 +87,7 @@ grub_cmd_videotest (grub_command_t cmd __attribute__ ((unused)),
       return grub_error (GRUB_ERR_BAD_FONT, "no font loaded");
 
     glyph = grub_font_get_glyph (fixed, '*');
-    grub_font_draw_glyph (glyph, color, 200 ,0);
+    grub_font_draw_glyph (glyph, color, 200, 0, 1);
 
     color = grub_video_map_rgb (255, 255, 255);
 
@@ -148,7 +148,7 @@ grub_cmd_videotest (grub_command_t cmd __attribute__ ((unused)),
       {
 	color = grub_video_map_color (i);
 	palette[i] = color;
-	grub_font_draw_glyph (glyph, color, 16 + i * 16, 220);
+	grub_font_draw_glyph (glyph, color, 16 + i * 16, 220, 1);
       }
   }
 
diff --git a/grub-core/font/font.c b/grub-core/font/font.c
index 24adcb35a..536cbde71 100644
--- a/grub-core/font/font.c
+++ b/grub-core/font/font.c
@@ -142,6 +142,8 @@ ascii_glyph_lookup (grub_uint32_t code)
 	  ascii_font_glyph[current]->offset_x = 0;
 	  ascii_font_glyph[current]->offset_y = -2;
 	  ascii_font_glyph[current]->device_width = 8;
+	  ascii_font_glyph[current]->scaled_bitmap = NULL;
+	  ascii_font_glyph[current]->scale = 0;
 	  ascii_font_glyph[current]->font = &null_font;
 
 	  grub_memcpy (ascii_font_glyph[current]->bitmap,
@@ -177,6 +179,8 @@ grub_font_loader_init (void)
   unknown_glyph->offset_x = 0;
   unknown_glyph->offset_y = -3;
   unknown_glyph->device_width = 8;
+  unknown_glyph->scaled_bitmap = NULL;
+  unknown_glyph->scale = 0;
   unknown_glyph->font = &null_font;
   grub_memcpy (unknown_glyph->bitmap,
 	       unknown_glyph_bitmap, sizeof (unknown_glyph_bitmap));
@@ -806,6 +810,8 @@ grub_font_get_glyph_internal (grub_font_t font, grub_uint32_t code)
       glyph->offset_x = xoff;
       glyph->offset_y = yoff;
       glyph->device_width = dwidth;
+      glyph->scaled_bitmap = NULL;
+      glyph->scale = 0;
 
       /* Don't try to read empty bitmaps (e.g., space characters).  */
       if (len != 0)
@@ -813,6 +819,7 @@ grub_font_get_glyph_internal (grub_font_t font, grub_uint32_t code)
 	  if (grub_file_read (font->file, glyph->bitmap, len) != len)
 	    {
 	      remove_font (font);
+	      grub_free (glyph->scaled_bitmap);
 	      grub_free (glyph);
 	      return 0;
 	    }
@@ -1559,10 +1566,19 @@ grub_font_construct_glyph (grub_font_t hinted_font,
 
   if (max_glyph_size < cur_glyph_size)
     {
-      grub_free (glyph);
+      if (glyph)
+	{
+	  grub_free (glyph->scaled_bitmap);
+	  grub_free (glyph);
+	}
       if (grub_mul (cur_glyph_size, 2, &max_glyph_size))
 	max_glyph_size = 0;
       glyph = max_glyph_size > 0 ? grub_malloc (max_glyph_size) : NULL;
+      if (glyph)
+	{
+	  glyph->scaled_bitmap = NULL;
+	  glyph->scale = 0;
+	}
     }
   if (!glyph)
     {
@@ -1571,9 +1587,12 @@ grub_font_construct_glyph (grub_font_t hinted_font,
       return main_glyph;
     }
 
+  grub_free (glyph->scaled_bitmap);
   grub_memset (glyph, 0, cur_glyph_size);
 
   glyph->font = main_glyph->font;
+  glyph->scaled_bitmap = NULL;
+  glyph->scale = 0;
   if (bounds.width == 0 || bounds.height == 0 ||
       grub_cast (bounds.width, &glyph->width) ||
       grub_cast (bounds.height, &glyph->height) ||
@@ -1598,12 +1617,55 @@ grub_font_construct_glyph (grub_font_t hinted_font,
   return glyph;
 }
 
+/*
+ * Scale the glyph bitmap by `scale` times.
+ * If succeeded, scaled bitmap will be stored at glyph->scaled_bitmap, and
+ * the corresponding scale factor will be stored at glyph->scale.
+ * If failed, glyph will not be touched.
+ */
+static void
+try_scale_glyph (struct grub_font_glyph *glyph, int scale)
+{
+  unsigned i, j, src_bit, dst_bit;
+  int pixel;
+  grub_uint16_t new_width, new_height;
+  grub_size_t bitmap_size;
+  grub_uint8_t *bitmap;
+
+  if (glyph->scale == scale)
+    return;
+
+  if (grub_mul (glyph->width, scale, &new_width) ||
+      grub_mul (glyph->height, scale, &new_height))
+    return;
+
+  if (grub_video_bitmap_calc_1bpp_bufsz (new_width, new_height, &bitmap_size))
+    return;
+  bitmap = grub_zalloc (bitmap_size);
+  if (bitmap == NULL)
+    return;
+
+  for (i = 0; i < new_height; i++)
+    for (j = 0; j < new_width; j++)
+      {
+	src_bit = (i / scale) * glyph->width + (j / scale);
+	dst_bit = i * new_width + j;
+	pixel = (glyph->bitmap[src_bit / 8] >> (7 - src_bit % 8)) & 1;
+	bitmap[dst_bit / 8] |= pixel << (7 - dst_bit % 8);
+      }
+  
+  grub_free (glyph->scaled_bitmap);
+  glyph->scaled_bitmap = bitmap;
+  glyph->scale = scale;
+}
+
 /* Draw the specified glyph at (x, y).  The y coordinate designates the
    baseline of the character, while the x coordinate designates the left
    side location of the character.  */
 grub_err_t
 grub_font_draw_glyph (struct grub_font_glyph * glyph,
-		      grub_video_color_t color, int left_x, int baseline_y)
+		      grub_video_color_t color, int left_x, int baseline_y,
+		      int scale)
 {
   struct grub_video_bitmap glyph_bitmap;
 
@@ -1636,11 +1698,28 @@ grub_font_draw_glyph (struct grub_font_glyph * glyph,
 			  &glyph_bitmap.mode_info.fg_alpha);
   glyph_bitmap.data = glyph->bitmap;
 
-  int bitmap_left = left_x + glyph->offset_x;
-  int bitmap_bottom = baseline_y - glyph->offset_y;
-  int bitmap_top = bitmap_bottom - glyph->height;
+  if (scale > 1)
+    try_scale_glyph (glyph, scale);
+
+  if (glyph->scale == scale)
+    {
+      glyph_bitmap.mode_info.width = glyph->width * scale;
+      glyph_bitmap.mode_info.height = glyph->height * scale;
+      glyph_bitmap.mode_info.pitch = glyph->width * scale;
+      glyph_bitmap.data = glyph->scaled_bitmap;
+    }
+  else
+    {
+      /* Scaled bitmap not suitable, fallback to no-scale.  */
+      scale = 1;
+    }
+
+  int bitmap_left = left_x + glyph->offset_x * scale;
+  int bitmap_bottom = baseline_y - glyph->offset_y * scale;
+  int bitmap_top = bitmap_bottom - glyph->height * scale;
 
   return grub_video_blit_bitmap (&glyph_bitmap, GRUB_VIDEO_BLIT_BLEND,
 				 bitmap_left, bitmap_top,
-				 0, 0, glyph->width, glyph->height);
+				 0, 0,
+				 glyph->width * scale, glyph->height * scale);
 }
diff --git a/grub-core/gfxmenu/font.c b/grub-core/gfxmenu/font.c
index 756c24f20..ed59ca954 100644
--- a/grub-core/gfxmenu/font.c
+++ b/grub-core/gfxmenu/font.c
@@ -67,7 +67,7 @@ grub_font_draw_string (const char *str, grub_font_t font,
 	  err = grub_errno;
 	  goto out;
 	}
-      err = grub_font_draw_glyph (glyph, color, x, baseline_y);
+      err = grub_font_draw_glyph (glyph, color, x, baseline_y, 1);
       if (err)
 	goto out;
       x += glyph->device_width;
diff --git a/grub-core/term/gfxterm.c b/grub-core/term/gfxterm.c
index 3c468f459..4512dee6f 100644
--- a/grub-core/term/gfxterm.c
+++ b/grub-core/term/gfxterm.c
@@ -656,7 +656,7 @@ paint_char (unsigned cx, unsigned cy)
   /* Render glyph to text layer.  */
   grub_video_set_active_render_target (text_layer);
   grub_video_fill_rect (bgcolor, x, y, width, height);
-  grub_font_draw_glyph (glyph, color, x, y + ascent);
+  grub_font_draw_glyph (glyph, color, x, y + ascent, 1);
   grub_video_set_active_render_target (render_target);
 
   /* Mark character to be drawn.  */
diff --git a/include/grub/font.h b/include/grub/font.h
index 708fa42ac..6417e5b58 100644
--- a/include/grub/font.h
+++ b/include/grub/font.h
@@ -79,6 +79,12 @@ struct grub_font_glyph
   /* Number of pixels to advance to start the next character.  */
   grub_uint16_t device_width;
 
+  /* Pointer to cached scaled bitmap.  Allocated during a scaling drawing.  */
+  grub_uint8_t *scaled_bitmap;
+
+  /* The scale factor for cached scaled bitmap.  */
+  int scale;
+
   /* Row-major order, packed bits (no padding; rows can break within a byte).
      The length of the array is (width * height + 7) / 8.  Within a
      byte, the most significant bit is the first (leftmost/uppermost) pixel.
@@ -141,7 +147,8 @@ struct grub_font_glyph *EXPORT_FUNC (grub_font_get_glyph_with_fallback) (grub_fo
 
 grub_err_t EXPORT_FUNC (grub_font_draw_glyph) (struct grub_font_glyph *glyph,
 					       grub_video_color_t color,
-					       int left_x, int baseline_y);
+					       int left_x, int baseline_y,
+					       int scale);
 
 int
 EXPORT_FUNC (grub_font_get_constructed_device_width) (grub_font_t hinted_font,
-- 
2.30.2