Fix ParticleMaterial scale on start() not correctly resetting

[RPicster]

This PR fixes #55396 by always resetting the scale when RESTART_ROT_SCALE is true (was already all there, just not used).

[clayjohn]

This only resets the scale of the matrix (kind of, it will change the rotation, but won't necessarily reset the rotation). See: https://download.brainvoyager.com/bv/doc/UsersGuide/CoordsAndTransforms/SpatialTransformationMatrices.html

[RPicster]

@clayjohn : It wasn't my intention to reset the rotation - I only wanted to reset scale as this was the cause for the bug.
The RESTART_ROT_SCALE was just a variable I am piggybacking that was already there but not used (and worked).
I don't think it is necessary to reset rotation as it can not lead to problems (that I know of).

[akien-mga]

Well I don't think we should re-use RESTART_ROT_SCALE if it's only handling scale and rotation. That's a hint that we should look into what RESTART_ROT_SCALE is/does and see if that's actually semantically correct to use it here, or if a new/different variable should be added.

It seems like in master at least RESTART_ROT_SCALE is never used. So if it's only use is to reset the scale only, it could be renamed (and the places where it gets set to true or false should be reviewed to make sure they match what this needs).

$ rg restart_rotation_scale
servers/rendering/renderer_rd/renderer_storage_rd.cpp
10060:          actions.renames["RESTART_ROT_SCALE"] = "restart_rotation_scale";

servers/rendering/renderer_rd/shaders/particles.glsl
245:    bool restart_rotation_scale = false;
320:                                    restart_rotation_scale = true;
392:                    restart_rotation_scale = true;

[akien-mga]

Bump :)

[clayjohn]

Taking a look now, to fix this we can just fully reset scale and rotation. Scale and rotation can't really be separated once baked into the transform which is likely why they are bundled together in the first place. In other words, there are situations where it makes sense to reset position without scale and rotation, but there likely aren't any places where it makes sense to reset scale but not rotation (and it may not even be possible)

Suggested change

	code += " TRANSFORM[0].x = 1.0;\n";
	code += " TRANSFORM[1].y = 1.0;\n";
	code += " TRANSFORM[2].z = 1.0;\n";
	code += " TRANSFORM[0] = vec4(1.0, 0.0, 0.0, 0.0);\n";
	code += " TRANSFORM[1] = vec4(0.0, 1.0, 0.0, 0.0);\n";
	code += " TRANSFORM[2] = vec4(0.0, 0.0, 1.0, 0.0);\n";

Issues were found after the initial approval, needs more work and re-review.

[clayjohn]

Superseded by #78021. Thanks for your contribution!