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Forums > C64 Coding > Simple bilinear interpolation in assembler
2018-05-08 16:24
Wertstahl

Registered: Apr 2012
Posts: 32
Simple bilinear interpolation in assembler

Hello,

for some reason, with increasing age, i am no longer interested in spending much time on re-inventing the wheel.

Therefore, i'd like to ask if any of you wizards perhaps know of a close solution to this problem:

Lets say you have a "heatmap" in a matrix of 20x10 cells.

Does anyone perhaps already have a fast and simple routine for interpolating all the values within these cells, so that when you have some cells with very high values and some cells with very low values, that more or less smooth transitions (image blur) can be achieved in very few rasterlines?

Google just spat out hardcore math for me, which i feel unable to wrap my head around, when attempted to translate to a c64 assembler solution. (I code in assembly, directly, no c++ or the like, pretty please).

best regards
WS
 
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2018-06-09 15:38
Sparta

Registered: Feb 2017
Posts: 12
(clc)
lda 03ff,x
adc 0401,x
ror
adc 0400,x
ror
sta 0400,x
adc 0402,x
ror
adc 0401,x
ror
sta 0401,x


Ps. Check out my fire effect in Tunnel Vision.
Edit. If unrolled, you can omit ,x indexing.
2018-06-09 16:39
Wertstahl

Registered: Apr 2012
Posts: 32
sparta, that looks very sleek. i was afraid that something like that, which i do not fully understand, might work. how did you come up with this solution?
2018-06-09 16:54
Sparta

Registered: Feb 2017
Posts: 12
Many many years of code optimization. :))

(JK, I am just a hobby coder)

Actually, I used something similar in my fire effect in Tunnel Vision. Except, I did not have enough memory to fully unroll the loop and I also modified the result using a cosine tab. In the fire effect, the 3rd addition comes from the char line below. Something like this:

0400=(((03ff+0401)/2)+0428)/2

When you add to 8-bit numbers, the result will be a 9-bit number with 1-8th bits in AR and the 9th bit in C. ROR will divide this 9-bit number by 2, rolling the C in AR. This will also modify C again, however, CLC can be safely omitted in most of the cases, because the difference in your result is <=1, and the next ROR will half that, too.
2018-06-09 16:54
Wertstahl

Registered: Apr 2012
Posts: 32


although the rol solution (above) also has this effect of smearing things into one direction, which i am currently trying to suppress so i can do everything in one go, using lookup tables: (having some brightness trouble currently, though)



way less easy than i thought.

(both images show a 4x3 cross and a 3x3 square blurred)


Oh! Thank you for your explanation Sparta! Much appreciated!
2018-06-09 16:59
Sparta

Registered: Feb 2017
Posts: 12
Double buffering will avoid the skew as you will not overwrite your original values.

Also, keep in mind the above solution is not a true average of the 3 values:

b=(a+2b+c)/4
2018-06-09 17:00
Wertstahl

Registered: Apr 2012
Posts: 32
And, because i didnt yet say what this is for: it is for a battle tactics ki precalculation. Now i said it.
2018-06-09 17:02
Wertstahl

Registered: Apr 2012
Posts: 32
Ah! I had a double buffering version before but for some reason fell back to single frame! Thanks alot for the hint! That should do the trick!
2018-06-09 17:13
Sparta

Registered: Feb 2017
Posts: 12
lda buffer1-1
adc buffer1+1
ror
adc buffer1
ror
sta buffer2

lda buffer1
adc buffer1+2
ror
adc buffer1+1
ror
sta buffer2+1


Put it in a loop if you want. Good luck!
2018-06-09 17:19
Sparta

Registered: Feb 2017
Posts: 12
If speed is not an issue, you may also want to try something like this to get an even better average of 4 neighboring values:

lda buffer1-1
adc buffer1+1
ror
sta ZP
lda buffer-$28
adc buffer+$28
ror
adc ZP
ror
sta buffer2
2018-06-09 17:47
Wertstahl

Registered: Apr 2012
Posts: 32
Oh man! This is so beautiful! Thank you!!!



http://dl.dataelephant.net/spartablur.prg

(press space to move)

http://dl.dataelephant.net/spartablur.rar
(requires cbmprgstudio to compile:
http:http://www.ajordison.co.uk/download.html )
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