c++ - Valid PointSize for QFont -

i have qopenglwidget in draw text qpainter. implement snapshot feature rendering widget content qopenglframebuffer , converting frame buffer qimage.

unfortunately, if set font's point size high (> 46), text appears black bar in snapshot, while in widget displayed correctly. see below example snapshot block on line supposed text font size > 46.

here simplified code render image (it should work, because correctly displayed in qopenglwidget):

void rendersomething(const int x, const int y, const qstring & str, const int fontsize) {     // 1. draw line     // (calculate min_x, max_x, y , z values)     gllinewidth(3);     glcolor3f(0., 0., 0.);     glbegin(gl_lines);     glvertex3f(min_x, y, z);     glvertex3f(max_x, y, z);     glend();      // 2. draw text     glint gl_viewport[4];     glgetintegerv(gl_viewport, gl_viewport);     backup_gl_state();     qopenglpaintdevice paintdevice(gl_viewport[2], gl_viewport[3]);     qpainter painter(&paintdevice);     painter.setfont(qfont(painter.font().family(), fontsize);     painter.setpen(qt::black);     painter.drawtext(x, y, str);     painter.end();     restore_gl_state(); } 

here code storing snapshot:

void viewport::takesnapshot(const qstring & path, const int size) {     glpushattrib(gl_viewport_bit);     glviewport(0, 0, size, size); // since size varies want text scale     qopenglframebufferobject fbo(size, size, qopenglframebufferobject::depth);     fbo.bind();     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      renderer.rendersomething(100, 100, "test", 50); // here render call!      qimage fboimage(fbo.toimage());     qimage image(fboimage.constbits(), fboimage.width(), fboimage.height(), qimage::format_rgb32);     image.save(path);     glpopattrib();     fbo.binddefault();     fbo.release(); } 

edit

i found workaround using qpainter directly draw text on qimage instead of drawing fbo. no black bar anymore, complicates code , happy find real solution...

the solution simple: re-read the documentation on qopenglframebufferobject in says:

create qopenglframebufferobject instance combineddepthstencil attachment if want qpainter render correctly.

i attached depth buffer. correct initialization be:

qopenglframebufferobject fbo(size, size, qopenglframebufferobject::combineddepthstencil);