Getting screen-space world origin in pixel shader?

[Jugbot]

I am trying to get the origin in a pixel shader in screen space but the origin is always the same value (I think it is always 0,0 but opengl makes it hard to tell)

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vec4 origin = TransformProjectionMatrix * vec4(0.0f, 0.0f, 0.0f, 1.0f);

I am using hump.camera and the camera tracks the player yet the origin does not seem to change.

[pgimeno]

No, the origin rarely changes in Löve 11.x because most transforms are done by the CPU, not the GPU. See the note in TransformMatrix here: Shader_Variables (it applies to TransformProjectionMatrix as well).

I believe it's a consequence of overzealous autobatching. Apparently it's done so the same batch can be used between matrix changes, yet I don't think it's common to keep drawing the same texture between matrix changes.

[Jugbot]

That is pretty weird since I am using the transform projection on the vertices and that has an effect, so I was expecting I was missing something basic

I am drawing with a quad.

[pgimeno]

If you leave only the projection and remove the transform (i.e. use only ProjectionMatrix), you'll probably obtain the same result. That means that the transform is a unit matrix and therefore has no effect.

The projection matrix is necessary to transform screen coordinates to normalized device coordinates (ranging from -1 to 1 in all axes). I don't think there's anything that changes it, so it's likely not considered for autobatching. I haven't looked into the related source, though, so I may be wrong.

[Jugbot]

What is the easiest way to draw a full screen pixel effect while still getting the transform matrix?

[pgimeno]

In 11.x I'm not sure if it's possible directly. Maybe if you render a spritebatch, not sure. Anyway, if you use the Löve transformation object (e.g. via cam11) you can pass the transform matrix to the shader; see Transform:getMatrix and Shader:send.