I got some RGB palette in a byte array which I'd like to convert or "map" to an RGB struct array, isn't this easily possible without using dozens of struct constructors?


RGB[256] PALETTE = cast(RGB[256]) [
    0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
    0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...

doesn't work cause of "non-constant expression"

RGB[256] PALETTE = (cast(RGB[]) [
    0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
    0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...
]) (0 .. 256);

compiles, but yields empty structs (and doesn't seem right anyway).

Just remembered the old casting hack:

RGB[] PALETTE = (cast(RGB*) cast(ubyte[]) [...])[0..256];

It works but is there perhaps another nicer possibility?

On Tue, 29 Dec 2009 07:56:04 -0500, Trass3r <mrmocool@gmx.de> wrote:

> I got some RGB palette in a byte array which I'd like to convert or "map" to an RGB struct array, isn't this easily possible without using dozens of struct constructors?
>
>
> RGB[256] PALETTE = cast(RGB[256]) [
>      0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
>      0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...
>
> doesn't work cause of "non-constant expression"
>
> RGB[256] PALETTE = (cast(RGB[]) [
>      0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
>      0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...
> ]) (0 .. 256);
>
> compiles, but yields empty structs (and doesn't seem right anyway).

What is RGB's structure?

I would expect something like this to work:

RGB[256] PALETTE = [
{0x00, 0x00, 0x00},
{0xE3, 0x53, 0x00},
...
];

Assuming RGB is a struct of 3 ubyte members...

-Steve

Steven Schveighoffer schrieb:
> What is RGB's structure?
> 
> I would expect something like this to work:
> 
> RGB[256] PALETTE = [
> {0x00, 0x00, 0x00},
> {0xE3, 0x53, 0x00},
> ...
> ];
> 
> Assuming RGB is a struct of 3 ubyte members...
> 

Yeah, simply 3 ubytes.
But IIRC I read that struct literals will be removed in D2 so I didn't test that approach.

On Tue, 29 Dec 2009 10:03:50 -0500, Trass3r <mrmocool@gmx.de> wrote:

> Steven Schveighoffer schrieb:
>> What is RGB's structure?
>>  I would expect something like this to work:
>>  RGB[256] PALETTE = [
>> {0x00, 0x00, 0x00},
>> {0xE3, 0x53, 0x00},
>> ...
>> ];
>>  Assuming RGB is a struct of 3 ubyte members...
>>
>
> Yeah, simply 3 ubytes.
> But IIRC I read that struct literals will be removed in D2 so I didn't test that approach.

You are right, I asked the question on that thread of whether it was worth keeping struct literals for this purpose.

-Steve

On Tue, 29 Dec 2009 10:37:43 -0500, Steven Schveighoffer <schveiguy@yahoo.com> wrote:

> On Tue, 29 Dec 2009 10:03:50 -0500, Trass3r <mrmocool@gmx.de> wrote:
>
>> Steven Schveighoffer schrieb:
>>> What is RGB's structure?
>>>  I would expect something like this to work:
>>>  RGB[256] PALETTE = [
>>> {0x00, 0x00, 0x00},
>>> {0xE3, 0x53, 0x00},
>>> ...
>>> ];
>>>  Assuming RGB is a struct of 3 ubyte members...
>>>
>>
>> Yeah, simply 3 ubytes.
>> But IIRC I read that struct literals will be removed in D2 so I didn't test that approach.
>
> You are right, I asked the question on that thread of whether it was worth keeping struct literals for this purpose.

And the answer (created by bearophile): http://codepad.org/8HnF62s2

-Steve

Trass3r wrote:
> I got some RGB palette in a byte array which I'd like to convert or "map" to an RGB struct array, isn't this easily possible without using dozens of struct constructors?
> 
> 
> RGB[256] PALETTE = cast(RGB[256]) [
>     0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
>     0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...
> 
> doesn't work cause of "non-constant expression"
> 
> RGB[256] PALETTE = (cast(RGB[]) [
>     0x00, 0x00, 0x00, 0xE3, 0x53, 0x00,
>     0xCF, 0x4B, 0x07, 0xBF, 0x43, 0x0F, ...
> ]) (0 .. 256);
> 
> compiles, but yields empty structs (and doesn't seem right anyway).

You've hit both an anti-feature and a bug.

First the anti-feature: [0xAB, ...] will yield an int[], not a ubyte[] (I guess ubyte[] is what you're expecting). If you cast two arrays, the compiler will reinterpret cast all data. The result won't be what you intended.

Second, the bug: casting arrays at compiletime seems to behave differently from casting at runtime. Casting at compiletime doesn't reinterpret cast, it does conversion! Demonstration here: http://codepad.org/OGjXADdu

Feel free to file some bug reports.

grauzone schrieb:
> First the anti-feature: [0xAB, ...] will yield an int[], not a ubyte[] (I guess ubyte[] is what you're expecting). If you cast two arrays, the compiler will reinterpret cast all data. The result won't be what you intended.
> 
Yeah I already encountered that problem. That's why I had to cast(ubyte[]) it (where conversion is expected) for my reinterpret casting:

RGB[] PALETTE = (cast(RGB*) cast(ubyte[]) [...])[0..256];


> Second, the bug: casting arrays at compiletime seems to behave differently from casting at runtime. Casting at compiletime doesn't reinterpret cast, it does conversion! Demonstration here: http://codepad.org/OGjXADdu
> 

You're right. But it only concerns casting to a struct(?) or an array of structs, right?!. Conversion is correct for standard arrays, but struct arrays need to be reinterpret cast (correct me if I'm wrong, I can't imagine how conversion could be reasonably used. Only thing might be casting an array of structs to another array of structs but I don't know any valid use-case).

Steven Schveighoffer schrieb:
>> You are right, I asked the question on that thread of whether it was worth keeping struct literals for this purpose.
> 
> And the answer (created by bearophile): http://codepad.org/8HnF62s2
> 

Yeah, I know but if you got that data out of some file like the resource section of a game exe in my case, adding the struct constructors is cumbersome.

grauzone schrieb:
> Second, the bug: casting arrays at compiletime seems to behave differently from casting at runtime. Casting at compiletime doesn't reinterpret cast, it does conversion! Demonstration here: http://codepad.org/OGjXADdu
> 
> Feel free to file some bug reports.

Just found out this is stated as a feature in the docs.
http://www.digitalmars.com/d/2.0/expression.html#ArrayLiteral

http://codepad.org/bvk63OPw