Re: [cc65] TGI pixel aspect ratio

On Donnerstag 29 Oktober 2009, Oliver Schmidt wrote:
> However I disagree with your statement that the 'pixel aspect ratio'
> is unrelated (not even talking about 'completely unrelated') to the
> resolution, size or aspect ratio of the display.

there is nothing to disagree really, its defined like that.

> Although theoretically the display aspect ratio and the pixel aspect
> ratio are of course different values they are in fact _directly_
> related to each other as soon as you have a fixed screen aspect ratio,

no. they are directly related if both the screen aspect ratio *and* the screen 
resolution is fixed.

> which is the case for all cc65 targets meant to display on (classic)
> TV screens or monitors with identical display aspect ratio. The Apple2
> and C128 are examples for this - sorry for not mentioning this fact
> ;-)

what about the lynx ? :) and no, infact its not fixed for other targets 
either, eg the c64 doesnt actually display a 4:3 image, since the actual 
image is surrounded by a border.

> In general a CRT display is generated by some pixel clock. And that
> pixel clock typically has a "normal" rate. That rate is typically
> adjusted to yield a pixel aspect ratio of ~1. Because of the fixed
> screen aspect ratio this directly results in a resolution aspect ratio
> similiar to a (classic) TV screen.

see above. for most (if not all) classic homecomputers this is not true, 
because of the borders.

> Result: There seem to be quite some interpretations what this thread
> is about. However my understanding of this thread is that the driver
> could/should basically provide the information if it runs the pixel
> clock at a rate resulting the usual ~1 pixel aspect ratio or if it
> runs at double/half speed.

why? this can be calculated from the information the driver already gives, 
like i showed in the previous post.

> I don't see any point in defining the aspect ratio of the display. The
> TGI API already has tgi_getxres() and tgi_getyres() which allow to do
> whatever necessary in that area.

see above.

> - Trying to adjust for those seems overengineering to me for a 6502
> program. 

thats bolloks. every decent circle routine since 1985 on the c64 takes it into 
account. (it must be taken into account if you dont want to make it look very 
strange and wrong)

> - Most cc65 programs run today in emulators just ignoring those
> deviation altogether.

and thats completely irrelevant imho. programs arent written for the emulator, 
atleast mine are not :)

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