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EnTerr
Level 8

How does DrawScaledObject() reduce images?

Does someone know how ifDraw2D.DrawScaledObject() scales images, in particular reducing an image?
(There are different algorithms possible)

Specifically, say i have scaleX and scaleY being 0.5 or 0.25 (i.e. reducing image 2x or 4x). Will each of the new pixels be a kind of "average" (bi-linear or bi-cubic interpolation over 4 or 16 pixels respectively) - or will it pick a single pixel (nearest-neighbour)?
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15 Replies
Komag
Level 9

Re: How does DrawScaledObject() reduce images?

You could set up an original image that is every other line red and green, and see what happens!

And maybe SetScaleMode(mode as Integer) changes it to one vs the other
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squirreltown
Level 9

Re: How does DrawScaledObject() reduce images?

"EnTerr" wrote:
Specifically, say i have scaleX and scaleY being 0.5 or 0.25 (i.e. reducing image 2x or 4x). Will each of the new pixels be a kind of "average" (bi-linear or bi-cubic interpolation over 4 or 16 pixels respectively) - or will it pick a single pixel (nearest-neighbour)?


I love your questions, I'm not optimistic about you getting an answer to this one. Just based on what i've seen happen, my guess is bicubic, with nearest-neighbor being the least likely. You can usually tell if its N-N, it really creates a lot of contrast that wasn't in the original.
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EnTerr
Level 8

Re: How does DrawScaledObject() reduce images?

"Komag" wrote:
You could set up an original image that is every other line red and green, and see what happens!
That occurred to me but will be unreliable, since depending on the model, different (>1) graphic engines are used. And even if i tested on every model in existence, results may be valid only in this point of time, today.

And maybe SetScaleMode(mode as Integer) changes it to one vs the other
You mean ifRegion.SetScaleMode()? I am not using roRegions, so not directly applicable but thanks for letting me know about its existence. Looking at the folksy description
"SetScaleMode(mode as Integer) as Void" wrote:

Set the scaling mode used for DrawScaledObject
  • 0 = fast scaling operation (may have jaggies)

  • 1 = smooth scaling operation (may be slow)

now i wonder (question #2):
Is it trying to say that 0 does nearest-neighbor and 1 does bilinear interpolation?
(Source for my speculation, the unrelated ifTextureRequest.SetScaleMode)
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Komag
Level 9

Re: How does DrawScaledObject() reduce images?

Ah, I never noticed "ifTextureRequest.SetScaleMode", sounds likely to be the same
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TheEndless
Level 7

Re: How does DrawScaledObject() reduce images?

"EnTerr" wrote:
You mean ifRegion.SetScaleMode()? I am not using roRegions, so not directly applicable but thanks for letting me know about its existence. Looking at the folksy description

<REDACTED>
EDIT: My assertion here was entirely incorrect, so removed here to avoid confusion in the future.

"EnTerr" wrote:
now i wonder (question #2):
Is it trying to say that 0 does nearest-neighbor and 1 does bilinear interpolation?
(Source for my speculation, the unrelated ifTextureRequest.SetScaleMode)

Yes, I believe so. There's a much more obvious visual difference on 3.1 firmwares than on 5.x+, but there's a significant speed improvement when using a scale mode of 0 on both. Generally speaking, I use a scale mode of 0 for animations, and a scale mode of 1 for static drawing. If the source needs to be scaled (to the same size) on every frame, then it's best to cache it to a bitmap, so you only need to do the scaling once.
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EnTerr
Level 8

Re: How does DrawScaledObject() reduce images?

"TheEndless" wrote:
Note that to use SetScaleMode, you set it on the target region, not the source. Even if you're not drawing to a specific region of your target, you can still wrap the whole bitmap in a region to take advantage of the scale modes (also applies to roScreen): ...

Thank you for the practical tips. The part about SetScaleMode() applying to the target region should be added to the docs, not obvious at all.

Do you have observations about performance penalty from extra wrapping a bitmap in a region? (ballpark. are we talking 0.3%, 3%, 30% etc)
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TheEndless
Level 7

Re: How does DrawScaledObject() reduce images?

<REDACTED>
EDIT: My assertion above was entirely incorrect, so removed here to avoid future confusion.

"EnTerr" wrote:
Do you have observations about performance penalty from extra wrapping a bitmap in a region? (ballpark. are we talking 0.3%, 3%, 30% etc)

I honestly can't say I've noticed any performance penalty, and I use regions for just about everything. I'd be interested in seeing the results of one of your infamous benchmark tests on it, though.. Smiley Wink
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NewManLiving
Level 7

Re: How does DrawScaledObject() reduce images?

i have never noticed it either and I also use them all the time
Would not think so since it is essentially a viewport.
Most importantly though is what a region can do.
1, It clips (can even make regions on roScreen)
So calculations occur only once prior to creating
The region, then the region itself has
It's own coordinate layout at 0,0. Don't forget the
Undocumented 2d interface which lends nicely to
The clipping
2, it scrolls wonderfully. Beats dragging bitmaps
Across the screen, especially on lower models
Giving a more smoother look and feel
It pretranslates , saving you from creating a complex
BS formula for us which woud be slower

There are other things it is useful for especially with
It's 2d interface

For the last 6 months I have been working on
A grid which mimics the best of some of the ones available
It is completed now and I am impressed on how well it performs
On the boxes that I have. I could not have done it without regions
Since the textures are coming and going all the time and the grid needed
To be updated even while the user is scrolling it. If I was not Offsetting regions
But changing the xy coordinates of the cells then each texture object would
Need to update itself with the new coordinates until the texture was received. With region
Offsettibg the bitmap is fixed and the region moves

So the point is that optimizing is relevant to what it can do
As opposed to how long it takes to create one
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NewManLiving
Level 7

Re: How does DrawScaledObject() reduce images?

By the way this grid is a perfect example
Of observing the texturemanagers lru
Caching. Textures initially pop in nicely
But with repeated scrolling they literally
Melt in at fast speeds although there is
No difference in the number released and
The number requested at any given time
My Channels: 2D API Framework Presentation: https://owner.roku.com/add/2M9LCVC
Updated: 11-11-2015 - Completed Keyboard interface
The Joel Channel ( Final Beta )
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