The point is, that i wanted to manipulate the point size not in object space but in pixels, hoever i counldn't find anything like that.
I would be so happy if one of you could tell me how to do that
Do the World/View/Projection multiplications first, and then add 'size' to the result. Note that your XY coordinates will be between -1.0 and +1.0 when on screen, so to add one pixel to the size, you need to add 1.0 / width on X and 1.0 / height on Y, where width and height are the dimensions of your viewport.
Thank you, but 1.0/width and 1.0/height seem to be too small...
The first visual results ( 1 Pixel ) I get when I multiply those values with 4, otherwise no triangle is drawn. Everything is set to screen resolution ( viewport, buffer width, projection matrix ). Is there any other thing i have to take care of?
For normal perspective projection it will be what Z was before the multiplication with the projection matrix, and the division is what actually brings the coordinates into [-1, 1] (if they're on screen).
The division will always be performed by D3D after your shader is run, but if you do it in the shader W/W = 1 and you output the coordinates exactly as their final values. Also this is what makes it possible to specify the size in pixels even if Z is not constant. If you draw in 2D and always use Z=1 for example you could skip the division.