Oh, yeah, the plotloop is a complete placeholder, just so I can compare output to the C prototype. That said, I'd done exactly the same thing on scf versus set 7,d in my line drawing code (don't worry: just once, outside the loop). I must find time to finish documenting my vector drawing code as I'm sure that would only benefit from being seen by somebody other than me.
The screen's at 32768 because I have multiplication tables occupying the highest and lowest 2kb of RAM. It's the usual squared and divided by 4 stuff, so by using that positioning I can do the relevant 16bit addition and subtraction in HL and then read the result directly from RAM without any further computation. On Sat, Oct 24, 2009 at 8:43 PM, Chris Pile <chris.p...@blueyonder.co.uk> wrote: > Just a quick glimps of the code shows you can save 8-clocks every > itteration of your plotloop by getting rid of the SET 7,D instructions > and putting a SCF before a RR D instruction. Replacing the SRL D's > with RR D's. > > But as you're not likely to be using this particular plotloop in the final > article it probably doesn't matter too much! > > That said, using SCF / RR D instead of SRL D / SET 7,D is something > worth remembering for later! > > Better still, keep your screens at address 0 and do away with the SCF's > altogether. > > Rearranging your registers so that you don't need to keep calculating the > screen address is always a good optimisation... But I take it you're going > to use the stack to shove the scanlines on-screen? Which is even better!! > > I've always been a big fan of using the stack!! :-)) > > Chris. > > > > > > @plotloop: > > ; left pixel > ld a, (hl) > inc h > > ; right pixel > ld c, (hl) > inc l > > dec h > > ld d, l > ld e, a > srl d > rr e > jr nc, @+rpx > > ld a, 0x0f > jr @+pxd > > @rpx: > ld a, 0xf0 > > @pxd: > set 7, d > ld (de), a > > ld d, l > ld e, c > srl d > rr e > jr nc, @+rpx > > ld a, 0x0e > jr @+pxd > > @rpx: > ld a, 0xe0 > > @pxd: > set 7, d > ld (de), a > > djnz @-plotloop > >
