Pixel Shader stage did not run

Question

I can't figure out why the pixel shader won't run. I'm using the Blinn-Phong per-pixel shader from here. Only change I've made is that I pass an aditional color per vertex which gets multiplied by the light-color in the pixel shader.

So far the Graphics Analyzer shows me a valid IA-result and the same (okay looking) result in the VS-stage. I disabled depth-stencil for testing and though everything looks rather fine I always see "Stage did not run. No output." when I inspect the captured frame.

This is my Projection-matrix:

_projection = Matrix.PerspectiveFovLH((float) Math.PI / 4.0f, viewports[0].Width / viewports[0].Height,
            0.1f, 100f);

Values are Width: 1346, Height: 800

My View is calculated like this:

_rotation = Quaternion.RotationYawPitchRoll(Yaw, Pitch, Roll);
Vector3.Transform(ref _target, ref _rotation, out _target);

Vector3 up = Vector3.UnitY;
Vector3.Transform(ref up, ref _rotation, out up);

_view = Matrix.LookAtLH(Position, _target, up);

Whereas Position: X:50, Y:50, Z:-300, Target: X:50, Y:50, Z:0 and Yaw, Pitch, Roll are all 0.

World-Matrix is currently Matrix.Identity.

The quad I try to render spans itself from X:0, Y:0 to X:100, Y:100 with 4 vertices and 6 indices.

I first thought that SV_POSITION must be a normalized value since it's obviously a SV-coordinate and someone posted in another thread that this solved his problem - but then the VS-stage does not show anything at all and PS still won't run.

It's been quite some years since I last worked with DirectX so I'm not sure anymore why this happens.

Answer 1

Your input w values are zeros.

The mathematical principles which projection matrices are based on rely on the input vector w element to be 1.0. The GPU later uses the resulting w element of each position vector to perform the perspective divide.

In your case, your projection cannot work (because you input w = 0) and the perspective divide is a divide-by-zero.