问题描述：
在windows下，当FLTK界面包含中文的时候，打开程序的时候会花费好几秒的时间才能完整显示界面
原因：
查了代码，最后发现原因在于绘制字符的时候通过GetTextExtentPoint32W这个函数获取字符宽度，由于这个函数本身速度不够快，所以FLTK使用缓存方式来保存宽度，问题在于缓存的方式不适合中文这种宽字符，当前的缓存方式是每当获取一个字符宽度时，把这个字符左右共1024个相邻字符的宽度提前获取并保存，以后每次获取字符宽度之前先搜索缓存，如果没有再通过API实际获取。
这个做法对于英文没有问题，因为GetTextExtentPoint32W处理英文的速度很快，而且一次获取1024个相邻字符基本就把程序可能会用到的字符全部囊括了，但是当界面出现中文的时候这种做法就出现问题了，中文的字符集是很大的，一次获取相邻个1024字符宽度并不能保证囊括了绝大多数的字符，所以每次界面显示之前都会花很多时间获取很多用不到的字符宽度，虽然显示一次之后的速度很快，但是启动程序的时候会出现卡顿
所以我做了修正，每当需要获取字符宽度的时候只保存当前字符的宽度，不获取相邻字符的宽度，这样就避免了问题
修正代码：
一共修改2个文件，当前修改的是FLTK3，如果要修改FLTK1.3.X，只要找到对应的代码即可
src/fltk3/font.h (fltk1.3.X对应的文件是src/fl_font.h)
class Fl_Font_Descriptor {
public:
...
# ifdef WIN32
HFONT fid;
int *width[64];
unsigned char *widthcached[64]; // 0-not cache, 1-cached //这里增加定义
...
};
src/fltk3/win32_font.cxx(fltk1.3.X对应的文件是src/fl_font_win32.cxx)
Fl_Font_Descriptor::Fl_Font_Descriptor(const char* name, fltk3::Fontsize fsize)
{
...
int i;
for (i = 0; i < 64; i++) {
width[i] = NULL;
widthcached[i] = NULL; // 这里增加
}
...
}
Fl_Font_Descriptor::~Fl_Font_Descriptor()
{
...
int i;
for (i = 0; i < 64; i++) {
if ( width[i] != NULL ) free(width[i]);
if ( widthcached[i] != NULL ) free(widthcached[i]); // 这里增加
}
}
double fltk3::GDIGraphicsDriver::width(unsigned int c) // 修改主体就是这个方法，具体代码如下
{
Fl_Font_Descriptor *fontsize = font_descriptor();
unsigned int r;
SIZE s;
// Special Case Handling of Unicode points over U+FFFF.
// The logic (below) computes a lookup table for char widths
// on-the-fly, but the table only covers codepoints up to
// U+FFFF, which covers the basic multilingual plane, but
// not any higher plane, or glyphs that require surrogate-pairs
// to encode them in WinXX, which is UTF16.
// This code assumes that these glyphs are rarely used and simply
// measures them explicitly if they occur - This will be slow...
if(c > 0x0000FFFF) { // UTF16 surrogate pair is needed
if (!fl_gc) { // We have no valid gc, so nothing to measure - bail out
return 0.0;
}
int cc; // cell count
unsigned short u16[4]; // Array for UTF16 representation of c
// Creates a UTF16 string from a UCS code point.
cc = fltk3::ucs_to_Utf16(c, u16, 4);
// Make sure the current font is selected before we make the measurement
SelectObject(fl_gc, fontsize->fid);
// measure the glyph width
GetTextExtentPoint32W(fl_gc, (WCHAR*)u16, cc, &s);
return (double)s.cx;
}
// else - this falls through to the lookup-table for glyph widths
// in the basic multilingual plane
r = (c & 0xFC00) >> 10;
unsigned short ii;
HDC gc;
HWND hWnd;
if (!fontsize->width[r]) {
fontsize->width[r] = (int*) malloc(sizeof(int) * 0x0400);
fontsize->widthcached[r] = (unsigned char *)malloc(sizeof(unsigned char) * 0x0400);
for (int k=0; k<0x0400; k++) fontsize->widthcached[r][k] = 0;
ii = r * 0x400;
// The following code makes a best effort attempt to obtain a valid fl_gc.
// If no fl_gc is available at the time we call fltk3::width(), then we first
// try to obtain a gc from the first fltk window.
// If that is null then we attempt to obtain the gc from the current screen
// using (GetDC(NULL)).
// This should resolve STR #2086
gc = fl_gc;
hWnd = 0;
if (!gc) { // We have no valid gc, try and obtain one
// Use our first fltk window, or fallback to using the screen via GetDC(NULL)
hWnd = fltk3::first_window() ? fl_xid(fltk3::first_window()) : NULL;
gc = GetDC(hWnd);
}
if (!gc) fltk3::fatal("Invalid graphic context: fltk3::width() failed because no valid HDC was found!");
SelectObject(gc, fontsize->fid);
ii += c &0x03FF;
GetTextExtentPoint32W(gc, (WCHAR*)&ii, 1, &s);
fontsize->width[r][c&0x03FF] = s.cx;
fontsize->widthcached[r][c&0x03FF] = 1;
if (gc && gc!=fl_gc) ReleaseDC(hWnd, gc);
//printf("[%d,%X]\n", s.cx, c);
} else {
if ( fontsize->widthcached[r][c&0x03FF] == 1 ) return (double) fontsize->width[r][c & 0x03FF];
ii = r * 0x400;
gc = fl_gc;
hWnd = 0;
if (!gc) { // We have no valid gc, try and obtain one
// Use our first fltk window, or fallback to using the screen via GetDC(NULL)
hWnd = fltk3::first_window() ? fl_xid(fltk3::first_window()) : NULL;
gc = GetDC(hWnd);
}
if (!gc) fltk3::fatal("Invalid graphic context: fltk3::width() failed because no valid HDC was found!");
SelectObject(gc, fontsize->fid);
ii += c &0x03FF;
GetTextExtentPoint32W(gc, (WCHAR*)&ii, 1, &s);
fontsize->width[r][c&0x03FF] = s.cx;
fontsize->widthcached[r][c&0x03FF] = 1;
if (gc && gc!=fl_gc) ReleaseDC(hWnd, gc);
//printf("[%d,%X]\n", s.cx, c);
}
return (double) fontsize->width[r][c & 0x03FF];
}