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Fix font hinting when using subpixel rendering 

Ensure we set the font's size with freetype to the intended size so that
hinting works as expected and perform subpixel scaling using affine
matrix coefficient.
This commit is contained in:
Francesco Abbate 2020-12-11 14:36:32 +01:00
parent 9114148b45
commit a41754b382
1 changed files with 8 additions and 11 deletions
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19
lib/font_renderer/font_renderer_alpha.h
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@ -81,20 +81,17 @@ public:
void set_font_height(double height) { void set_font_height(double height) {
const double scale_x = (m_prescale_x ? 100.0 : 1.0); const double scale_x = (m_prescale_x ? 100.0 : 1.0);
m_feng.height(height); m_feng.height(height);
if (m_subpixel) { m_feng.width(height * scale_x);
const int subpixel_scale = 3;
m_feng.width(height * scale_x * subpixel_scale);
} else {
m_feng.width(height * scale_x);
}
} }
template<class Rasterizer, class Scanline, class RenSolid> template<class Rasterizer, class Scanline, class RenSolid>
void draw_codepoint(Rasterizer& ras, Scanline& sl, void draw_codepoint(Rasterizer& ras, Scanline& sl,
RenSolid& ren_solid, const color_type color, RenSolid& ren_solid, const color_type color,
int codepoint, double& x, double& y, int subpixel_scale) int codepoint, double& x, double& y, const int subpixel_scale)
{ {
const double scale_x = (m_prescale_x ? 100.0 : 1.0); const double scale_x = (m_prescale_x ? 100.0 : 1.0);
// Coefficient to scale back the glyph to the final scale.
const double cx_inv_scale = subpixel_scale / scale_x;
// Represent the delta in x scaled by scale_x. // Represent the delta in x scaled by scale_x.
double x_delta = 0; double x_delta = 0;
@ -114,15 +111,15 @@ public:
double ty = m_hinting ? floor(y + 0.5) : y; double ty = m_hinting ? floor(y + 0.5) : y;
ras.reset(); ras.reset();
m_mtx.reset(); m_mtx.reset();
m_mtx *= agg::trans_affine_scaling(1.0 / scale_x, 1); m_mtx *= agg::trans_affine_scaling(cx_inv_scale, 1);
m_mtx *= agg::trans_affine_translation(start_x + x_delta / scale_x, ty); m_mtx *= agg::trans_affine_translation(start_x + cx_inv_scale * x_delta, ty);
ras.add_path(m_trans); ras.add_path(m_trans);
ren_solid.color(color); ren_solid.color(color);
agg::render_scanlines(ras, sl, ren_solid); agg::render_scanlines(ras, sl, ren_solid);
} }
y += glyph->advance_y; y += glyph->advance_y;
x += (x_delta + glyph->advance_x) / scale_x; x += cx_inv_scale * (x_delta + glyph->advance_x);
} }
} }
@ -135,7 +132,7 @@ public:
void render_codepoint(agg::rendering_buffer& ren_buf, void render_codepoint(agg::rendering_buffer& ren_buf,
const color_type text_color, const color_type text_color,
double& x, double& y, double& x, double& y,
int codepoint, int subpixel_scale) int codepoint, const int subpixel_scale)
{ {
if (!m_font_loaded) { if (!m_font_loaded) {
return; return;