Re: [cc65] TGI pixel aspect ratio

On Mittwoch 28 Oktober 2009, Oliver Schmidt wrote:
> Hi Groepaz,
>
> > good test to make sure wether this actually works: write a portable
> > program that draws a circle. a circle thats an actual circle and not an
> > elipse that is :) (personally i dont see this working without lots of
> > effort)
>
> _That_ seems overengineering to me. 

no its not :) its exactly what pixel aspect ratio would be used/needed for.

> Something much more simple instead: 
>
> The 3dmaze currently looks like this on the C128:
> http://img02.imagefra.me/img/img02/2/10/28/f_q0nm_1774e25.png
>
> Then I faked the feature we're discussing here with:
>
> #ifdef __C128__
> #define ASPECT 2
> #else
> #define ASPECT 1
> #endif
>
> Using then the ASPECT macro it took me a little as 2 (!) minutes to
> change 3dmaze to look like this on the C128:
> http://img03.imagefra.me/img/img03/2/10/28/f_oqym_f698d8e.png
>
> See what I mean ? ;-))

yes, see my other post. what you mean is NOT pixel aspect ratio :) pixel 
aspect ratio refers to a SINGLE pixel, it is completely unrelated to the 
resolution, size, or aspect ratio of the display. both the c64 (hires mode) 
and the VDC have a pixel aspect ratio of ~ 1. (not quite obvious for the VDC, 
indeed - but "pixel" doesnt include the black space between actual pixels).

to achive what you are talking about, it makes more sence to me to define the 
aspect ratio of the DISPLAY (that can be done in a macro, i dont think any of 
the targets can change it). then what you need can be calculated from the 
display resolution:

#define DAX 4
#define DAY 3

vic/hires:       (320/DAX)/(200/DAY)== 80/66.6==1.2
vic/multicolor:  (160/DAX)/(200/DAY)== 40/66.6==0.6
vdc:             (640/DAX)/(200/DAY)==160/66.6==2.4

(or whatever other calculation, for stretching like you did you might want to 
do it differently, and make it so that you dont get fractions < 1, and so you 
get seperate factors for X and Y)

this wouldnt only be correct without confusing the terminology, it would also 
not need any extra code :)

sorry to be pedantic about this.... but after extensivly reading up on the 
subject years ago (because i was doing image processing/converting) all the 
confusion and half-accurate things "out there" make me protest :)

-- 

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Man kann garnicht so dumm denken wie es manchmal kommt.

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