Hello,

is there any way to get the pixel color of a single pixel by x and y coordinates of a context?

On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
> Hello,
>
> is there any way to get the pixel color of a single pixel by x and y coordinates of a context?

render to a png back buffer.

see cairo_image_surface_create_for_data

then you'll be able to access the data and, at the same time, to blit your buffer to screen.

On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>> Hello,
>>
>> is there any way to get the pixel color of a single pixel by x and y coordinates of a context?
>
> render to a png back buffer.
>
> see cairo_image_surface_create_for_data
>
> then you'll be able to access the data and, at the same time, to blit your buffer to screen.

Thanks for your answer. But how do i access the function via the context?

It does not work like this:

class DW:DrawingArea{
	this(){
		addOnDraw(&drawCallback);
	}
	bool drawCallback(Scoped!Context cr, Widget widget){
		char[] c = new char[](256*256);
		auto val = cr.cairo_image_surface_create_for_data(c,cairo_format_t.CAIRO_FORMAT_ARGB32, 256,256, cairo.format_stride_for_width(cairo_format_t.CAIRO_FORMAT_ARGB32,256));
		return true;
	}
}
"no property 'cairo_image_surface_create_for_data' for type 'Scoped'"

On 01/01/2016 01:37 PM, TheDGuy wrote:
> On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
>> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>>> Hello,
>>>
>>> is there any way to get the pixel color of a single pixel by x and y
>>> coordinates of a context?
>>
>> render to a png back buffer.
>>
>> see cairo_image_surface_create_for_data
>>
>> then you'll be able to access the data and, at the same time, to blit
>> your buffer to screen.
>
> Thanks for your answer. But how do i access the function via the context?
>
> It does not work like this:
>
> class DW:DrawingArea{
>      this(){
>          addOnDraw(&drawCallback);
>      }
>      bool drawCallback(Scoped!Context cr, Widget widget){
>          char[] c = new char[](256*256);
>          auto val =
> cr.cairo_image_surface_create_for_data(c,cairo_format_t.CAIRO_FORMAT_ARGB32,
> 256,256,
> cairo.format_stride_for_width(cairo_format_t.CAIRO_FORMAT_ARGB32,256));
>          return true;
>      }
> }
> "no property 'cairo_image_surface_create_for_data' for type 'Scoped'"

you would either cr.getTarget(); or cairo.ImageSurface.ImageSurface.create.

I'm not sure how those would get you access to the pixel data.

-- 
Mike Wey

On Friday, 1 January 2016 at 15:22:18 UTC, Mike Wey wrote:
> On 01/01/2016 01:37 PM, TheDGuy wrote:
>> [...]
>
> you would either cr.getTarget(); or cairo.ImageSurface.ImageSurface.create.
>
> I'm not sure how those would get you access to the pixel data.

Okay, thanks for your answer.

So which function do i call with "cr.getTarget()" and how can i get the rgb-values of a pixel from it?

On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>> Hello,
>>
>> is there any way to get the pixel color of a single pixel by x and y coordinates of a context?
>
> render to a png back buffer.
>
> see cairo_image_surface_create_for_data
>
> then you'll be able to access the data and, at the same time, to blit your buffer to screen.


Actually I was thinking to a user defined buffer type:

struct SurfaceBuffer
{
    void* data; // used as param to create the surface
    Rgba[] opIndex(size_t index);
    Rgba[][] scanline();
}

that you would pass as data in cairo_image_surface_create_for_data().

But gtk certainly has pitcure classes with the typical scanline method and that you could use in cairo_image_surface_create_for_data.

On Friday, 1 January 2016 at 19:32:40 UTC, Basile B. wrote:
> On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
>> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>>> Hello,
>>>
>>> is there any way to get the pixel color of a single pixel by x and y coordinates of a context?
>>
>> render to a png back buffer.
>>
>> see cairo_image_surface_create_for_data
>>
>> then you'll be able to access the data and, at the same time, to blit your buffer to screen.
>
>
> Actually I was thinking to a user defined buffer type:
>
> struct SurfaceBuffer
> {
>     void* data; // used as param to create the surface
>     Rgba[] opIndex(size_t index);
>     Rgba[][] scanline();
> }
>
> that you would pass as data in cairo_image_surface_create_for_data().
>
> But gtk certainly has pitcure classes with the typical scanline method and that you could use in cairo_image_surface_create_for_data.

Ahm, i am not quite sure if you and [Mike Wey] talk about the same thing. And i posted the error message in my last post when i try to call "cairo_image_surface_create_for_data". I still don't know where i am able to call the function?

On Friday, 1 January 2016 at 22:00:04 UTC, TheDGuy wrote:
> On Friday, 1 January 2016 at 19:32:40 UTC, Basile B. wrote:
>> On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
>>> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>>>> Hello,
>>>>
>>>> is there any way to get the pixel color of a single pixel by x and y coordinates of a context?
>>>
>>> render to a png back buffer.
>>>
>>> see cairo_image_surface_create_for_data
>>>
>>> then you'll be able to access the data and, at the same time, to blit your buffer to screen.
>>
>>
>> Actually I was thinking to a user defined buffer type:
>>
>> struct SurfaceBuffer
>> {
>>     void* data; // used as param to create the surface
>>     Rgba[] opIndex(size_t index);
>>     Rgba[][] scanline();
>> }
>>
>> that you would pass as data in cairo_image_surface_create_for_data().
>>
>> But gtk certainly has pitcure classes with the typical scanline method and that you could use in cairo_image_surface_create_for_data.
>
> Ahm, i am not quite sure if you and [Mike Wey] talk about the same thing. And i posted the error message in my last post when i try to call "cairo_image_surface_create_for_data". I still don't know where i am able to call the function?

I took a look into the source code of cairo and in the "ImageSurface.d"-file there is a function called "createForData" but if i try to use it like this:

cairo.ImageSurface.createForData(c,cairo.FORMAT_ARGB32,256,256,256*4);

i get: "undefined identifier 'createForData' in module 'cairo.ImageSurface'

That is just one example of my experience using D:

some things are easy to understand but in other cases: even if you think it should work and you can proof it, it just doesn't or you have to do it in a really inconvenient way. I am getting frustrated

On 01/02/2016 12:32 AM, TheDGuy wrote:
> On Friday, 1 January 2016 at 22:00:04 UTC, TheDGuy wrote:
>> On Friday, 1 January 2016 at 19:32:40 UTC, Basile B. wrote:
>>> On Wednesday, 30 December 2015 at 23:20:23 UTC, Basile B. wrote:
>>>> On Wednesday, 30 December 2015 at 20:44:44 UTC, TheDGuy wrote:
>>>>> Hello,
>>>>>
>>>>> is there any way to get the pixel color of a single pixel by x and
>>>>> y coordinates of a context?
>>>>
>>>> render to a png back buffer.
>>>>
>>>> see cairo_image_surface_create_for_data
>>>>
>>>> then you'll be able to access the data and, at the same time, to
>>>> blit your buffer to screen.
>>>
>>>
>>> Actually I was thinking to a user defined buffer type:
>>>
>>> struct SurfaceBuffer
>>> {
>>>     void* data; // used as param to create the surface
>>>     Rgba[] opIndex(size_t index);
>>>     Rgba[][] scanline();
>>> }
>>>
>>> that you would pass as data in cairo_image_surface_create_for_data().
>>>
>>> But gtk certainly has pitcure classes with the typical scanline
>>> method and that you could use in cairo_image_surface_create_for_data.
>>
>> Ahm, i am not quite sure if you and [Mike Wey] talk about the same
>> thing. And i posted the error message in my last post when i try to
>> call "cairo_image_surface_create_for_data". I still don't know where i
>> am able to call the function?
>
> I took a look into the source code of cairo and in the
> "ImageSurface.d"-file there is a function called "createForData" but if
> i try to use it like this:
>
> cairo.ImageSurface.createForData(c,cairo.FORMAT_ARGB32,256,256,256*4);
>
> i get: "undefined identifier 'createForData' in module 'cairo.ImageSurface'

```
import cairo.ImageSurface;
ImageSurface.createForData(c,cairo.FORMAT_ARGB32,256,256,256*4);
```

You need to import the ImageSurface module, and the createForData function is in the ImageSurface class which is in the cairo.ImageSurface module.


> That is just one example of my experience using D:
>
> some things are easy to understand but in other cases: even if you think
> it should work and you can proof it, it just doesn't or you have to do
> it in a really inconvenient way. I am getting frustrated

-- 
Mike Wey

> ```
> import cairo.ImageSurface;
> ImageSurface.createForData(c,cairo.FORMAT_ARGB32,256,256,256*4);
> ```
>
> You need to import the ImageSurface module, and the createForData function is in the ImageSurface class which is in the cairo.ImageSurface module.

Thanks, that was the problem!

Now i can read the buffer from a png image and save the buffer as a file:

		auto pngImage = ImageSurface.createFromPng("C:\\Users\\Standardbenutzer\\Desktop\\DSC00564-1.png");
		auto buffer = pngImage.getData();
		auto cS = ImageSurface.createForData(buffer, cairo_format_t.ARGB32,pngImage.getWidth(),pngImage.getHeight(),pngImage.getStride());
		cS.writeToPng("test.png");

but how do i do that with my GTKD Context in my "drawCallback()" function?