Fix #108500: Resolve Metal line loop emulation for armature limits #108512

Jason Fielder · 2023-06-01T13:00:51+02:00

Jason Fielder commented

2023-06-01 13:00:51 +02:00

Authored by Apple: Michael Parkin-White

Jason Fielder added 1 commit 2023-06-01 13:01:00 +02:00

af030e03b6 Fix #108500 : Resolve Metal line loop emulation for armature limits

Authored by Apple: Michael Parkin-White

Jason Fielder requested review from Jeroen Bakker 2023-06-01 13:01:31 +02:00

Iliya Katushenock added this to the EEVEE & Viewport project 2023-06-01 14:21:55 +02:00

Iliya Katushenock added the

Interest

Animation & Rigging

label 2023-06-01 14:22:03 +02:00

Gaia Clary commented

2023-06-01 14:34:13 +02:00

@Jason-Fielder Thanks for the quick fix!!! I just copied the fix into my local blender and it worked for me. One thing: In the code the final line is treated differently. With the fix it looks to me like all lines could be treated in the same way, so the loop could go over all lines... no?

Michael Parkin-White commented

2023-06-01 14:39:39 +02:00

First-time contributor

@GaiaClary The purpose of the code is to emulate a LineLoop primitive type using LineList, as Metal does not support LineLoop natively.
This is achieved by using an index buffer to re-use existing vertex buffer data. The final line is different as it needs to create an additional line primitive between the last and first vertex. The other lines create a unique primitive between each two vertices.

For a LineLoop primitive, there is only one item of data specified for each "point" connecting lines, whereas a LineList has an explicit start and end for each line. So the index buffer repeats data points to specify two indices per primitive, which map to the original list of single points.

So if you have a line loop with 5 points (v0, v1, v2, v3, v4), you get 6 line segments. To represent this with a line list, you need to specify two points for each segment:

v0- > v1
v1 -> v2
v2 -> v3
v3 -> v4
v4 -> v5
and the closing line (which is handled slightly differently):
v5 -> v0.

@GaiaClary The purpose of the code is to emulate a LineLoop primitive type using LineList, as Metal does not support LineLoop natively. This is achieved by using an index buffer to re-use existing vertex buffer data. The final line is different as it needs to create an additional line primitive between the last and first vertex. The other lines create a unique primitive between each two vertices. For a LineLoop primitive, there is only one item of data specified for each "point" connecting lines, whereas a LineList has an explicit start and end for each line. So the index buffer repeats data points to specify two indices per primitive, which map to the original list of single points. So if you have a line loop with 5 points (v0, v1, v2, v3, v4), you get 6 line segments. To represent this with a line list, you need to specify two points for each segment: v0- > v1 v1 -> v2 v2 -> v3 v3 -> v4 v4 -> v5 and the closing line (which is handled slightly differently): v5 -> v0.

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Fix #108500: Resolve Metal line loop emulation for armature limits #108512