Merging points efficiently
From my post regarding indexing, you could see how using 'indexes' could help reduce the amount of points.
As an example. Consider a 3D box. I has 8 corners. All lines and triangles use these 8 corners, but a box is constructed by 12 lines and 12 triangles. Each line has 2 points and each triangle has 3. With each point taking 3 numbers, the amount of numbers stored to show a box is:
(12*2 + 12*3)*3 = 180 numbers.
If we store the 8 corner points separately (8*3 = 24 numbers) and simply store offsets/indices, the "*3" from the previous equation can be removed, resulting in:
24 + (12*2 + 12*3) = 84 numbers.
Parts in the LDraw library (especially standard parts) have a lot of common points, so it makes sense to use this trick to save memory, and thereby also rendering time. In our example above we save roughly 50%, so let us take a look at how much we can save in our test model.
I would also like to introduce you to an additional test model. This is the very first LDraw model I ever built. It is quite big (3500+ parts) and is good for stress testing:
![[Image: 112.png]](https://brickhub.org/i/data/112/112.png)
Here are the baseline numbers for just showing triangles and not using our trick to combine points. I call the two models 'Psych' (the blue car) and 'Executor':
Psych: Memory usage: 36.3MB. [color=#000000]Rendering time: 1.039ms. Number of points: [color=#000000]375.432.[/color][/color]
Executor: Memory usage: 862MB. [color=#000000]Rendering time: 1.8185ms. Number of points: [color=#000000]11.333.253.[/color][/color]
[color=#000000][color=#000000]This is what happens when you combine points for the full models:[/color][/color]
[color=#000000][color=#000000]Psych: Memory usage: [color=#000000][color=#000000]16.6MB. Rendering time: [color=#000000]3.121ms. Number of points: [color=#000000]99.687.[/color][/color][/color]
[/color][/color][/color]
Executor: Memory usage: [color=#000000]313MB. Rendering time: [color=#000000]99.495ms. Number of points: [color=#000000]2.700.145.[/color][/color][/color]
[color=#000000][color=#000000][color=#000000]That rendering time is completely unacceptable. Here is what happens when points are only combined for the individual parts (not the full mode:[/color][/color][/color]
[color=#000000][color=#000000][color=#000000][color=#000000][color=#000000]Psych: Memory usage: [color=#000000][color=#000000][color=#000000]20.5MB[/color]. Rendering time: [color=#000000][color=#000000]1.584ms.[/color] Number of points: [color=#000000][color=#000000]100.339[/color].[/color][/color][/color][/color][/color][/color]
[/color][/color][/color]
Executor: Memory usage: [color=#000000][color=#000000]414MB[/color]. Rendering time: [color=#000000][color=#000000]17.096ms[/color]. Number of points: [color=#000000][color=#000000]2.751.714[/color].[/color][/color][/color]
These tradeoffs are much more acceptable. Next up was adding normal lines to the mix.
From my post regarding indexing, you could see how using 'indexes' could help reduce the amount of points.
As an example. Consider a 3D box. I has 8 corners. All lines and triangles use these 8 corners, but a box is constructed by 12 lines and 12 triangles. Each line has 2 points and each triangle has 3. With each point taking 3 numbers, the amount of numbers stored to show a box is:
(12*2 + 12*3)*3 = 180 numbers.
If we store the 8 corner points separately (8*3 = 24 numbers) and simply store offsets/indices, the "*3" from the previous equation can be removed, resulting in:
24 + (12*2 + 12*3) = 84 numbers.
Parts in the LDraw library (especially standard parts) have a lot of common points, so it makes sense to use this trick to save memory, and thereby also rendering time. In our example above we save roughly 50%, so let us take a look at how much we can save in our test model.
I would also like to introduce you to an additional test model. This is the very first LDraw model I ever built. It is quite big (3500+ parts) and is good for stress testing:
Here are the baseline numbers for just showing triangles and not using our trick to combine points. I call the two models 'Psych' (the blue car) and 'Executor':
Psych: Memory usage: 36.3MB. [color=#000000]Rendering time: 1.039ms. Number of points: [color=#000000]375.432.[/color][/color]
Executor: Memory usage: 862MB. [color=#000000]Rendering time: 1.8185ms. Number of points: [color=#000000]11.333.253.[/color][/color]
[color=#000000][color=#000000]This is what happens when you combine points for the full models:[/color][/color]
[color=#000000][color=#000000]Psych: Memory usage: [color=#000000][color=#000000]16.6MB. Rendering time: [color=#000000]3.121ms. Number of points: [color=#000000]99.687.[/color][/color][/color]
[/color][/color][/color]
Executor: Memory usage: [color=#000000]313MB. Rendering time: [color=#000000]99.495ms. Number of points: [color=#000000]2.700.145.[/color][/color][/color]
[color=#000000][color=#000000][color=#000000]That rendering time is completely unacceptable. Here is what happens when points are only combined for the individual parts (not the full mode:[/color][/color][/color]
[color=#000000][color=#000000][color=#000000][color=#000000][color=#000000]Psych: Memory usage: [color=#000000][color=#000000][color=#000000]20.5MB[/color]. Rendering time: [color=#000000][color=#000000]1.584ms.[/color] Number of points: [color=#000000][color=#000000]100.339[/color].[/color][/color][/color][/color][/color][/color]
[/color][/color][/color]
Executor: Memory usage: [color=#000000][color=#000000]414MB[/color]. Rendering time: [color=#000000][color=#000000]17.096ms[/color]. Number of points: [color=#000000][color=#000000]2.751.714[/color].[/color][/color][/color]
These tradeoffs are much more acceptable. Next up was adding normal lines to the mix.