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Fix error with glyphs subpixel layout

This commit is contained in:
Francesco Abbate 2021-03-05 22:43:15 +01:00
parent 877e4ac6e2
commit 7abb36e5e8
1 changed files with 27 additions and 10 deletions
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37
lib/font_renderer/font_renderer.cpp
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@ -163,8 +163,17 @@ static void glyph_lut_convolution(agg::rendering_buffer ren_buf, agg::lcd_distri
gli.xoff -= 1;
}
static int ceil_to_multiple(int n, int p) {
return p * ((n + p - 1) / p);
// The two functions below are needed because in C and C++ integer division
// is rounded toward zero.
// euclidean division rounded toward positive infinite
static int div_pos(int n, int p) {
return n >= 0 ? (n + p - 1) / p : (n / p);
}
// euclidean division rounded toward negative infinite
static int div_neg(int n, int p) {
return n >= 0 ? (n / p) : ((n - p + 1) / p);
}
FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
@ -181,9 +190,11 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
// When using subpixel font rendering it is needed to leave a padding pixel on the left and on the right.
// Since each pixel is composed by n subpixel we set below x_start to subpixel_scale instead than zero.
// In addition we need one more pixel on the left because of subpixel positioning so
// it adds up to 2 * subpixel_scale.
// Note about the coordinates: they are AGG-like so x is positive toward the right and
// y is positive in the upper direction.
const int x_start = subpixel_scale;
const int x_start = 2 * subpixel_scale;
const agg::alpha8 text_color(0xff);
#ifdef FONT_RENDERER_HEIGHT_HACK
const int font_height_reduced = (font_height * 86) / 100;
@ -215,6 +226,8 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
x_size_sum += bounds[i].x2 - bounds[i].x1;
glyph_count++;
}
bounds[i].x1 = subpixel_scale * div_neg(bounds[i].x1, subpixel_scale);
bounds[i].x2 = subpixel_scale * div_pos(bounds[i].x2, subpixel_scale);
}
}
@ -240,7 +253,9 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
if (gbounds.x2 < gbounds.x1) continue;
// 1. It is very important to ensure that the x's increment below (1) and in
// (2), (3) and (4) are perfectly the same.
if (x + gbounds.x2 + 3 * subpixel_scale >= pixels_width * subpixel_scale) {
// Note that x_step below is always an integer multiple of subpixel_scale.
const int x_step = gbounds.x2 + 2 * subpixel_scale;
if (x + x_step >= pixels_width * subpixel_scale) {
x = x_start;
y = y_bottom;
}
@ -248,7 +263,7 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
const int glyph_y_bottom = y - 2 * pad_y - (gbounds.y2 - gbounds.y1);
y_bottom = (y_bottom > glyph_y_bottom ? glyph_y_bottom : y_bottom);
// 2. Ensure x's increment is aligned with (1)
x = x + gbounds.x2 + 3 * subpixel_scale;
x = x + x_step;
}
agg::int8u *cover_swap_buffer = (agg::int8u *) malloc(sizeof(agg::int8u) * (pixels_width * subpixel_scale));
@ -279,12 +294,16 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
y = pixels_height - 1;
y_bottom = y;
for (int i = 0; i < num_chars; i++) {
// Important: the variable x in this loop should always be an integer multiple
// of subpixel_scale.
int codepoint = first_char + index[i];
const agg::rect_i& gbounds = bounds[index[i]];
if (gbounds.x2 < gbounds.x1) continue;
// 3. Ensure x's increment is aligned with (1)
if (x + gbounds.x2 + 3 * subpixel_scale >= pixels_width * subpixel_scale) {
// Note that x_step below is always an integer multiple of subpixel_scale.
const int x_step = gbounds.x2 + 2 * subpixel_scale;
if (x + x_step >= pixels_width * subpixel_scale) {
// No more space along x, begin writing the row below.
x = x_start;
y = y_bottom;
@ -297,15 +316,13 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
double x_next = x, y_next = y_baseline;
renderer_alpha.render_codepoint(ren_buf, text_color, x_next, y_next, codepoint, subpixel_scale);
int x_next_i = (subpixel_scale == 1 ? int(x_next + 1.0) : ceil_to_multiple(x_next + 0.5, subpixel_scale));
// Below x and x_next_i will always be integer multiples of subpixel_scale.
// The y coordinate for the glyph below is positive in the bottom direction,
// like is used by Lite's drawing system.
FR_Bitmap_Glyph_Metrics& glyph_info = glyphs[index[i]];
glyph_info.x0 = x / subpixel_scale;
glyph_info.y0 = pixels_height - 1 - (y_baseline + gbounds.y2 + pad_y);
glyph_info.x1 = x_next_i / subpixel_scale;
glyph_info.x1 = div_pos(x_next + 0.5, subpixel_scale);
glyph_info.y1 = pixels_height - 1 - (y_baseline + gbounds.y1 - pad_y);
glyph_info.xoff = 0;
@ -322,7 +339,7 @@ FR_Bitmap *FR_Bake_Font_Bitmap(FR_Renderer *font_renderer, int font_height,
// When subpixel is activated we need one padding pixel on the left and on the right
// and one more because of subpixel positioning.
// 4. Ensure x's increment is aligned with (1)
x = x + gbounds.x2 + 3 * subpixel_scale;
x = x + x_step;
}
free(index);