Re: computing image axis limits

[Ben Abbott]

On Oct 2, 2010, at 3:34 PM, Shai Ayal wrote:

> On Sat, Oct 2, 2010 at 5:08 PM, Ben Abbott <address@hidden> wrote:
>> On Oct 2, 2010, at 1:31 AM, Shai Ayal wrote:
>> 
>>> Hi all.
>>> 
>>> Images with a width and/or height of 1 do not display correctly in the
>>> fltk backend as reported in the following bug report:
>>> https://savannah.gnu.org/bugs/?31093
>>> 
>>> The problem turned out to be bugs with the way image axis limits were
>>> calculated for images where width and/or height was 1.
>>> Axis limits for images are a bit tricky as they have to take the image
>>> pixel size into account. It turns out that today the image pixel size
>>> is be calculated in 4 different places:
>>> 1) opengl_renderer::draw_image
>>> 2) image::properties:update_{x,y}data
>>> 3) image.m: __img__
>>> 4) axis.m: __get_tight_lims__
>>> 
>>> As far as I could see, the calculation in (1) is correct. The attached
>>> patch (not a changeset yet!) fixes a bug in (2) and also adds a small
>>> fix for (3). with it, the following commands:
>>> backend fltk
>>> h=image (ones (1,8));
>>> 
>>> does not set the axis right, The image is clipped and so nothing shows
>>> up (this can be verified by set (h , "clipping" , "off")).
>>> 
>>> I am not sure how to approach the fixing of (3) and (4). Maybe we
>>> should consolidate the calculation for 3,4? maybe we should
>>> consolidate 1,2,3,4?
>>> 
>>> Shai
>>> <image1.patch>
>> 
>> I like the idea of consolidating the calculation for all cases.
>> 
> OK. How do we do I do it then?
> IMHO The best way would be to add a property to the image object which
> would hold this data, but it would have to be hidden since there is no
> equivalent matlab property.
> Another way would be to create a function which accepts the image
> handle and returns the pixel size
> 
> Shai


I have a copy of ML to play with. I'll need to experiment with various image 
sizes and values or xdata/ydata before I can offer an informed opinion on the 
detail.

I hope to have time for that later today.

Ben