c++ - Center bitmap text to a rectangle with OpenGL -

i need center piece of text rectangle.

i found example, i'm struggling understand does.

it not hard achieve this, need know how find width , height of text after being drawn, cannot find anywhere.

to draw text, char char:

static void drawtext(std::string str, float x, float y, float z) {     glrasterpos3f(x, y, z);     (unsigned int = 0; < str.size(); i++) {         glutbitmapcharacter(glut_bitmap_helvetica_18, str[i]);     } } 

not sure if best way, first program using opengl.

raster fonts awful, not work in modern opengl know - need use texture-mapped triangles implement bitmap fonts now-a-days. if starting out, legacy opengl may work you, find things raster pos not supported in opengl es , core opengl 3+.

that said can sum glutbitmapwidth (...) across of characters in string, this:

      unsigned int str_pel_width = 0; const unsigned int str_len       = str.size ();  // finding string length can expensive depending on implementation (e.g. in //   c-string requires looping through entire string storage until //     first null byte found, each , every time call this). // //  string has constant-length, move out of loop better //    performance! using std::string, not big issue, //      did ask "best way" of doing something.  (unsigned int = 0; < str_len; i++)   str_pel_width += glutbitmapwidth (glut_bitmap_helvetica_18, str [i]); 

now, finish discussion, should aware height of each character identical in glut bitmap font. if recall, 18 pt. helvetica 22 or 24 pixels high. distinction between pt. size , pixel size supposed dpi scaling, glut not implement this.