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Add some explanatory comments

This commit is contained in:
Francesco Abbate 2020-06-04 17:17:10 +02:00
parent dc5b668389
commit 67124de130
1 changed files with 10 additions and 9 deletions
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19
src/font_renderer.cpp
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@ -146,6 +146,8 @@ int FontRendererBakeFontBitmap(FontRenderer *font_renderer, int font_height,
const int y_step = font_height + 2 * pad_y;
agg::rendering_buffer ren_buf((agg::int8u *) pixels, pixels_width * subpixel_scale, pixels_height, -pixels_width * subpixel_scale * pixel_size);
// 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.
const int x_start = subpixel_scale;
int x = x_start, y = pixels_height;
int res = 0;
@ -233,19 +235,18 @@ void blend_solid_hspan_rgb_subpixel(agg::rendering_buffer& rbuf, agg::gamma_lut<
const agg::rgba8& c,
const agg::int8u* covers)
{
// const int subpixel_scale = 3;
// FIXME: rowlen à verifier
// unsigned rowlen = rbuf.width() * subpixel_scale;
// FIXME: no correct boundary limits for cx and cx_max
// int cx = (x_lcd - 2 >= 0 ? -2 : -x_lcd);
// int cx_max = (len + 2 <= rowlen ? len + 1 : rowlen - 1);
const int pixel_size = 4;
// cx being negative here and cx_max greater than 'len' means we will
// adress the 'covers' array beyond its formal limits here [0, len-1] by -subpixel_scale on the
// left and +subpixel_scale on the right.
// We assume it is safe to do so because the data are coming from FontRendererBakeFontBitmap
// and this latter function leaves three padding pixels on the left and on the right of the buffer.
int cx = -2;
int cx_max = len + 1;
const int x_min = floor_div(x_lcd + cx, 3);
const int x_max = floor_div(x_lcd + cx_max, 3);
const int pixel_size = 4;
const agg::int8u rgb[3] = { c.r, c.g, c.b };
agg::int8u* p = rbuf.row_ptr(y) + x_min * pixel_size;
@ -261,7 +262,7 @@ void blend_solid_hspan_rgb_subpixel(agg::rendering_buffer& rbuf, agg::gamma_lut<
unsigned src_col = gamma.dir(*(p + pixel_index[i]));
*(p + pixel_index[i]) = gamma.inv((((dst_col - src_col) * alpha) + (src_col << 16)) >> 16);
}
//p[3] = 0xff;
// Leave p[3], the alpha channel value unmodified.
p += 4;
}
}
@ -277,7 +278,7 @@ void FontRendererBlendGamma(FontRenderer *font_renderer, uint8_t *dst, int dst_s
}
}
// destination implicitly BGRA32. Source implictly single-byte renderer_alpha coverage.
// destination implicitly BGRA32. Source implictly single-byte renderer_alpha coverage with subpixel scale = 3.
void FontRendererBlendGammaSubpixel(FontRenderer *font_renderer, uint8_t *dst, int dst_stride, uint8_t *src, int src_stride, int region_width, int region_height, FontRendererColor color) {
const int subpixel_scale = 3;
agg::gamma_lut<>& gamma = font_renderer->gamma();