Hi,
I want to draw gray scale bitmap using byte array which has pixel by pixel gray scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very slow and I think there should be faster way of creating a Form using above byte array.
Anyone can help me? Thanks in advance.
On 11.06.2014, at 00:36, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Hi,
I want to draw gray scale bitmap using byte array which has pixel by pixel gray scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very slow and I think there should be faster way of creating a Form using above byte array.
If the width is a multiple of 4, you can use the byte array directly as form bits:
| w h bytes form | w := 100. h := 60. bytes := ((1 to: w*h) collect: [:i | 256 atRandom - 1]) asByteArray. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
This would be the best and fastest way. If the width is not a multiple of 4 then perhaps you can add the necessary padding when creating the byte array. Otherwise, a very fast way is to use BitBlt to copy whole lines from the byte array to the form.
But even creating a byte array with the right padding just using at:put: would be a lot faster than using a Pen.
- Bert -
Form has some class side methods to create Forms from arrays, too.
Cheers, Karl
On Wed, Jun 11, 2014 at 12:41 PM, Bert Freudenberg bert@freudenbergs.de wrote:
On 11.06.2014, at 00:36, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Hi,
I want to draw gray scale bitmap using byte array which has pixel by
pixel gray
scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very
slow and
I think there should be faster way of creating a Form using above byte
array.
If the width is a multiple of 4, you can use the byte array directly as form bits:
| w h bytes form | w := 100. h := 60. bytes := ((1 to: w*h) collect: [:i | 256 atRandom - 1]) asByteArray. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
This would be the best and fastest way. If the width is not a multiple of 4 then perhaps you can add the necessary padding when creating the byte array. Otherwise, a very fast way is to use BitBlt to copy whole lines from the byte array to the form.
But even creating a byte array with the right padding just using at:put: would be a lot faster than using a Pen.
- Bert -
Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners
Thanks you for your answer, however there is something I missed here.
I've tried following code
| w h bytes form | w := 200. h := 200. bytes := ((1 to: w*h) collect: [:i | 255 ]) asByteArray. (1 to: w) do: [ :x | (1 to: h) do: [ :y | x = y ifTrue: [ bytes at: (w*(y - 1) + x) put: 0 ] ] ]. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
What I expected is diagonal line but the result is not. What's wrong with my code?
Thank you in advance.
On Wed, Jun 11, 2014 at 7:41 PM, Bert Freudenberg bert@freudenbergs.de wrote:
On 11.06.2014, at 00:36, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Hi,
I want to draw gray scale bitmap using byte array which has pixel by
pixel gray
scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very
slow and
I think there should be faster way of creating a Form using above byte
array.
If the width is a multiple of 4, you can use the byte array directly as form bits:
| w h bytes form | w := 100. h := 60. bytes := ((1 to: w*h) collect: [:i | 256 atRandom - 1]) asByteArray. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
This would be the best and fastest way. If the width is not a multiple of 4 then perhaps you can add the necessary padding when creating the byte array. Otherwise, a very fast way is to use BitBlt to copy whole lines from the byte array to the form.
But even creating a byte array with the right padding just using at:put: would be a lot faster than using a Pen.
- Bert -
Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners
Ah, endianness issue, isn't it fun! BitBlt really operates on 32-bit words, so 4 pixels of your 8-bit form are stuffed into one word. And they are big-endian by default. You can indicate little-endian forms by using a negative depth. So, if you use -8 for your form depth it works.
You are (probably) on an x86 processor, which is little-endian, so your byte array's first byte ends up in the least significant byte of the first word. Interpreting that as a big-endian word gives the pattern you noticed.
I should have mentioned that stuffing a byte array into a form is a hack (there is even a method Form>>hackBits:). It is a useful hack, see for example Bitmap>>asByteArray. But by looking at that method you see you need to pay attention to your CPU's endianness:
Smalltalk isLittleEndian ==> true
Your code could use this:
Smalltalk isLittleEndian ifTrue: [form swapEndianness].
(or initialize its depth to 8 or -8 depending on endianness).
The "proper" way would be to use a "bitPoker", which is independent of endianness, but considerably slower:
| w h bytes form poker | w := 200. h := 200. bytes := ((1 to: w*h) collect: [:i | 255 ]) asByteArray. 1 to: w do: [ :x | 1 to: h do: [ :y | x = y ifTrue: [ bytes at: (w*(y - 1) + x) put: 0 ] ] ]. form := ColorForm extent: w@h depth: 8. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). poker := BitBlt bitPokerToForm: form. 0 to: w-1 do: [ :x | 0 to: h-1 do: [ :y | poker pixelAt: x@y put: (bytes at: w * y + x + 1). ] ]. form display
(Btw, don't put parens into "1 to: w do:". It works but defeats an important optimization).
- Bert -
On 12.06.2014, at 02:32, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Thanks you for your answer, however there is something I missed here.
I've tried following code
| w h bytes form | w := 200. h := 200. bytes := ((1 to: w*h) collect: [:i | 255 ]) asByteArray. (1 to: w) do: [ :x | (1 to: h) do: [ :y | x = y ifTrue: [ bytes at: (w*(y - 1) + x) put: 0 ] ] ]. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
What I expected is diagonal line but the result is not. What's wrong with my code?
Thank you in advance.
On Wed, Jun 11, 2014 at 7:41 PM, Bert Freudenberg bert@freudenbergs.de wrote: On 11.06.2014, at 00:36, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Hi,
I want to draw gray scale bitmap using byte array which has pixel by pixel gray scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very slow and I think there should be faster way of creating a Form using above byte array.
If the width is a multiple of 4, you can use the byte array directly as form bits:
| w h bytes form | w := 100. h := 60. bytes := ((1 to: w*h) collect: [:i | 256 atRandom - 1]) asByteArray. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
This would be the best and fastest way. If the width is not a multiple of 4 then perhaps you can add the necessary padding when creating the byte array. Otherwise, a very fast way is to use BitBlt to copy whole lines from the byte array to the form.
But even creating a byte array with the right padding just using at:put: would be a lot faster than using a Pen.
- Bert -
Thank you very much, especially to:do: part. This improves performance of my code(other part) considerably!
Sent from my iPad
On Jun 12, 2014, at 7:12 PM, Bert Freudenberg bert@freudenbergs.de wrote:
Ah, endianness issue, isn't it fun! BitBlt really operates on 32-bit words, so 4 pixels of your 8-bit form are stuffed into one word. And they are big-endian by default. You can indicate little-endian forms by using a negative depth. So, if you use -8 for your form depth it works.
You are (probably) on an x86 processor, which is little-endian, so your byte array's first byte ends up in the least significant byte of the first word. Interpreting that as a big-endian word gives the pattern you noticed.
I should have mentioned that stuffing a byte array into a form is a hack (there is even a method Form>>hackBits:). It is a useful hack, see for example Bitmap>>asByteArray. But by looking at that method you see you need to pay attention to your CPU's endianness:
Smalltalk isLittleEndian ==> true
Your code could use this:
Smalltalk isLittleEndian ifTrue: [form swapEndianness].
(or initialize its depth to 8 or -8 depending on endianness).
The "proper" way would be to use a "bitPoker", which is independent of endianness, but considerably slower:
| w h bytes form poker | w := 200. h := 200. bytes := ((1 to: w*h) collect: [:i | 255 ]) asByteArray. 1 to: w do: [ :x | 1 to: h do: [ :y | x = y ifTrue: [ bytes at: (w*(y - 1) + x) put: 0 ] ] ]. form := ColorForm extent: w@h depth: 8. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). poker := BitBlt bitPokerToForm: form. 0 to: w-1 do: [ :x | 0 to: h-1 do: [ :y | poker pixelAt: x@y put: (bytes at: w * y + x + 1). ] ]. form display
(Btw, don't put parens into "1 to: w do:". It works but defeats an important optimization).
- Bert -
On 12.06.2014, at 02:32, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Thanks you for your answer, however there is something I missed here.
I've tried following code
| w h bytes form | w := 200. h := 200. bytes := ((1 to: w*h) collect: [:i | 255 ]) asByteArray. (1 to: w) do: [ :x | (1 to: h) do: [ :y | x = y ifTrue: [ bytes at: (w*(y - 1) + x) put: 0 ] ] ]. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
What I expected is diagonal line but the result is not. What's wrong with my code?
Thank you in advance.
On Wed, Jun 11, 2014 at 7:41 PM, Bert Freudenberg bert@freudenbergs.de wrote: On 11.06.2014, at 00:36, Sungjin Chun chunsj@castlesoft.co.kr wrote:
Hi,
I want to draw gray scale bitmap using byte array which has pixel by pixel gray scale value as byte like this;
[0 0 0 0 0 0 0 0 16 23 255 78 12 12 12 12 ... ...] (8x4 for example)
I can draw this using Pen class pixel by pixel manner but this is very slow and I think there should be faster way of creating a Form using above byte array.
If the width is a multiple of 4, you can use the byte array directly as form bits:
| w h bytes form | w := 100. h := 60. bytes := ((1 to: w*h) collect: [:i | 256 atRandom - 1]) asByteArray. form := ColorForm extent: w@h depth: 8 bits: bytes. form colors: ((0 to: 255) collect: [:i | Color gray: i / 255]). form display
This would be the best and fastest way. If the width is not a multiple of 4 then perhaps you can add the necessary padding when creating the byte array. Otherwise, a very fast way is to use BitBlt to copy whole lines from the byte array to the form.
But even creating a byte array with the right padding just using at:put: would be a lot faster than using a Pen.
- Bert -
Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners
beginners@lists.squeakfoundation.org
-
Bert Freudenberg -
karl ramberg -
Sungjin Chun -
Sungjin Chun