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Cairo/Pango: compute character widths fast and string widths accurately

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This commit has Fl_Cairo_Graphics_Driver compute string widths in 2 ways:
1) when the string contains several unicode characters, the width of the
whole string is computed, accounting for kerning when it occurs;
2) when the string contains a single unicode character, its width is
computed, memorised, and re-used next time it's necessary.

The effect of this approach is
- Fl_Text_Display is fast because it uses memorised single character widths repeatedly
- Fl_Input is drawn accurately because the cursor position is determined
by string widths, not by sums of character widths.
This commit is contained in:
ManoloFLTK 2023-01-04 17:23:13 +01:00
parent d3988f9bdc
commit 13f2ea664a
2 changed files with 32 additions and 30 deletions
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2
src/drivers/Cairo/Fl_Cairo_Graphics_Driver.H
View File

@ -50,7 +50,7 @@ private:
bool *needs_commit_tag_; // NULL or points to whether cairo surface was drawn to
cairo_t *dummy_cairo_; // used to measure text width before showing a window
int linestyle_;
int width_unscaled_(unsigned int c);
int do_width_unscaled_(const char* str, int n);
protected:
cairo_t *cairo_;
PangoContext *pango_context_;

60
src/drivers/Cairo/Fl_Cairo_Graphics_Driver.cxx
View File

@ -1236,31 +1236,13 @@ void Fl_Cairo_Graphics_Driver::rtl_draw(const char* str, int n, int x, int y) {
}
double Fl_Cairo_Graphics_Driver::width(const char* c, int n) {
if (!font_descriptor()) return -1.0;
int i = 0, w = 0, l;
const char *end = c + n;
unsigned int ucs;
while (i < n) {
ucs = fl_utf8decode(c + i, end, &l);
i += l;
w += width_unscaled_(ucs);
}
return w / double(PANGO_SCALE);
}
double Fl_Cairo_Graphics_Driver::width(unsigned int c) {
return width_unscaled_(c)/ double(PANGO_SCALE);
}
int Fl_Cairo_Graphics_Driver::width_unscaled_(unsigned int c) {
unsigned int r = 0;
// cache the widths of single Unicode characters
double Fl_Cairo_Graphics_Driver::width(unsigned int utf32) {
unsigned r=0;
Fl_Cairo_Font_Descriptor *desc = NULL;
if (c <= 0xFFFF) { // when inside basic multilingual plane
if (utf32 <= 0xFFFF) {
desc = (Fl_Cairo_Font_Descriptor*)font_descriptor();
r = (c & 0xFC00) >> 10;
r = (utf32 & 0xFC00) >> 10;
if (!desc->width) {
desc->width = (int**)new int*[64];
memset(desc->width, 0, 64*sizeof(int*));
@ -1269,17 +1251,37 @@ int Fl_Cairo_Graphics_Driver::width_unscaled_(unsigned int c) {
desc->width[r] = (int*)new int[0x0400];
for (int i = 0; i < 0x0400; i++) desc->width[r][i] = -1;
} else {
if ( desc->width[r][c & 0x03FF] >= 0 ) { // already cached
return desc->width[r][c & 0x03FF];
if ( desc->width[r][utf32&0x03FF] >= 0 ) { // already cached
return desc->width[r][utf32 & 0x03FF] / double(PANGO_SCALE);
}
}
}
char buf[4];
int n = fl_utf8encode(c, buf);
pango_layout_set_text(pango_layout_, buf, n);
char buf4[4];
int n = fl_utf8encode(utf32, buf4);
int width = do_width_unscaled_(buf4, n);
if (utf32 <= 0xFFFF) {
desc->width[r][utf32 & 0x03FF] = width;
}
return width / double(PANGO_SCALE);
}
double Fl_Cairo_Graphics_Driver::width(const char* str, int n) {
if (!font_descriptor()) return -1;
if (n == fl_utf8len(*str)) { // str contains a single unicode character
int l;
unsigned c = fl_utf8decode(str, str+n, &l);
return width(c); // that character's width may have been cached
}
return do_width_unscaled_(str, n) / double(PANGO_SCALE); // full width computation for multi-char strings
}
int Fl_Cairo_Graphics_Driver::do_width_unscaled_(const char* str, int n) {
if (!n) return 0;
pango_layout_set_text(pango_layout_, str, n);
PangoRectangle p_rect;
pango_layout_get_extents(pango_layout_, NULL, &p_rect);
if (c <= 0xFFFF) desc->width[r][c & 0x03FF] = p_rect.width;
return p_rect.width;
}