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Volume Object Data Render Step Size cannot be reset back to 0 once changed.
Closed, ResolvedPublicBUG

Description

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 470/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13

Blender Version
Broken: version: 2.83 (sub 9), branch: master, commit date: 2020-03-18 23:24, hash: rB271231f58ee3
Worked: Never, it was added in 7537cad5761e

Short description of error
If the Step Size setting in the Render sub panel of the Volume Object Data tab is changed from it's default of 0, it cannot be changed back to 0

Exact steps for others to reproduce the error

  1. Start with the default scene.
  2. Switch the render engine to Cycles.
  3. Add a Volume object (even an empty one will do.)
  4. Change the Step Size setting in the Render sub panel of the Volume Object Data tab to anything other than the default of 0.
  5. Now try to change it back to 0

In the file below I have already done the first 4 steps for you.

In rna_gen_volume.c, I believe it is line 1070 where the minimum value is set to 0.0010000000f or 0.0000100000f based upon my experimenting.

FloatPropertyRNA rna_VolumeRender_step_size = {
	{(PropertyRNA *)&rna_VolumeRender_clipping, (PropertyRNA *)&rna_VolumeRender_space,
	-1, "step_size", 1, 0, 0, 4, 0, "Step Size",
	"Distance between volume samples. Higher values render more detail at the cost of performance. If set to zero, the step size is automatically determined based on voxel size",
	0, "*",
	PROP_FLOAT, PROP_DISTANCE | PROP_UNIT_LENGTH, NULL, 0, {0, 0, 0}, 0,
	rna_Volume_update_display, 0, NULL, NULL, rna_property_override_diff_default, rna_property_override_store_default, rna_property_override_apply_default,
	offsetof(VolumeRender, step_size), 5, NULL},
	VolumeRender_step_size_get, VolumeRender_step_size_set, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, 0.0010000000f, 100.0f, 0.0000100000f, FLT_MAX, 1.0f, 3, 0.0f, NULL
};