> On 11 Nov 2014, at 12:17, Nuno Santos <nunosan...@imaginando.pt> wrote: > > Hi, > > I want to give a flashing effect on a quad. My idea is to draw two quads. One > with the base color, and one above it with a white color but with > transparency oscillating. This will give the flashing effect. > > I’m not being able to do it with QSGVertexColorMaterial. There is no opacity > on quad there is placed above. I have found the following post answer but I > still can’t understand it quite well. > > "The blend mode used by the scene graph is glBlendFunc(GL_ONE, > GL_ONE_MINUS_SRC_ALPHA) which gives you premultiplied blending. A “valid” > color in premultiplied mode must have r <= a (same for g and b of course). If > it doesn’t, then that color channel will overflow, giving you additive > blending instead.” > > Will it be possible to implement this with a QSGVertexColorMaterial? > > // quad below > > v[0].set(_rect.left(), _rect.bottom(), r, g, b, a); > v[1].set(_rect.left(), _rect.top(), r, g, b, a); > v[2].set(_rect.right(), _rect.top(), r, g, b, a); > > v[3].set(_rect.left(), _rect.bottom(), r, g, b, a); > v[4].set(_rect.right(), _rect.top(), r, g, b, a); > v[5].set(_rect.right(), _rect.bottom(), r, g, b, a); > > // flashing quad above > > a=128+128*qSin(phase),r=0xff,g=0xff,b=0xff; > > v[6].set(_rect.left(), _rect.bottom(), r, g, b, a);
v[6].set(_rect.left(), _rect.bottom(), r * a, g * a, b * a, a ); Use premultiplied alpha as the docs state, otherwise you will end up getting something closer to additive blending which is not what you are after in this case. cheers, Gunnar > v[7].set(_rect.left(), _rect.top(), r, g, b, a); > v[8].set(_rect.right(), _rect.top(), r, g, b, a); > > v[9].set(_rect.left(), _rect.bottom(), r, g, b, a); > v[10].set(_rect.right(), _rect.top(), r, g, b, a); > v[11].set(_rect.right(), _rect.bottom(), r, g, b, a); > > Thanks, > > Regards, > > Nuno > > > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
