Acorn Arcade forums: Programming: OS_ScreenMode problem
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OS_ScreenMode problem |
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ksattic (07:35 28/5/2008)
VincceH (09:36 28/5/2008)
ksattic (18:14 28/5/2008)
Phlamethrower (18:46 28/5/2008)
VincceH (19:16 28/5/2008)
jmb (10:28 28/5/2008)
monkeyson2 (12:00 28/5/2008)
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Simon Wilson |
Message #107516, posted by ksattic at 07:35, 28/5/2008 |
 Finally, an avatar!
Posts: 1291
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OK, what am I doing wrong?
The following works:
int *mode_block;
r.r[0] = 1;
_kernel_swi(OS_ScreenMode, &r, &r);
mode_block = (int *)r.r[1];
The following does not:
int *mode_block;
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, (int)mode_block);
I am on cold medication and think I may just be missing the obvious...
Using gcc 4.1.1 prerelease 1 with UnixLib. |
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VinceH |
Message #107517, posted by VincceH at 09:36, 28/5/2008, in reply to message #107516 |
 Lowering the tone since the dawn of time
Posts: 1600
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OK, what am I doing wrong? Don't know, because I use _kernel_swi (as per your first example) rather than _swix, with which I am totally unfamiliar - but I can have a guess:
The following works:
int *mode_block;
r.r[0] = 1;
_kernel_swi(OS_ScreenMode, &r, &r);
mode_block = (int *)r.r[1]; And in that you are performing the cast of r.r[1] to how you typed mode_block.
The following does not:
int *mode_block;
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, (int)mode_block); In this, although you've typed mode_block in the same way as above, in the _swix call, you're casting mode_block to match the register (ie the exact opposite of what you did in the first example).
But given that you want r.r[1] put into int *mode_block (and here my unfamiliarity with _swix comes in) I doubt you can do it that way.
Would that not be similar to saying:
int *foo;
int bar;
(int *)bar=foo;
Which, AFAIK, will not work.
However, as I said, completely unfamiliar with how _swix works, so this is just a guess. |
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JMB |
Message #107518, posted by jmb at 10:28, 28/5/2008, in reply to message #107516 |
Member
Posts: 467
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int *mode_block;
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, (int)mode_block);
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, &mode_block); |
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Phil Mellor |
Message #107519, posted by monkeyson2 at 12:00, 28/5/2008, in reply to message #107516 |
 Please don't let them make me be a monkey butler
Posts: 12380
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Shouldn't you use OSLib for this sort of thing? |
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Simon Wilson |
Message #107525, posted by ksattic at 18:14, 28/5/2008, in reply to message #107517 |
Finally, an avatar!
Posts: 1291
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Would that not be similar to saying:
int *foo;
int bar;
(int *)bar=foo; It's similar to doing:
bar = (int)foo;
...which is legal. I was merely casting a pointer to an int, since _swix takes ints for its register values. The address still points at a value, but it is stored in an int instead of in an int *.
The reason why my second method doesn't work is because OS_ScreenMode wants to give me a pointer to a block that it has allocated, but all I am letting it do is change the value of the int that mode_block points at, but it is not pointing at a valid address. Using a double pointer or taking the address of mode_block allows the pointer to be changed.
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, &mode_block); Ah, that makes sense. It is giving me a pointer to a block.
Shouldn't you use OSLib for this sort of thing? That would be sensible!
I haven't tried linking OSLib into IyonixMesa yet, and I only need to do a very small amount of windowing stuff to support multitasking 3D apps. I'll give it a go.
[Edited by ksattic at 18:19, 28/5/2008]
[Edited by ksattic at 18:20, 28/5/2008] |
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Jeffrey Lee |
Message #107526, posted by Phlamethrower at 18:46, 28/5/2008, in reply to message #107525 |
 Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot Hot stuff
Posts: 15100
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Have you tried doing whatever magic is necessary to link IyonixMesa into SDL? A version of SDL for RISC OS which has OpenGL support could be a convenient way of getting a whole load of free 3D games ported (Including the inevitable SDL-OpenGL version of DeathDawn) |
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VinceH |
Message #107527, posted by VincceH at 19:16, 28/5/2008, in reply to message #107525 |
Lowering the tone since the dawn of time
Posts: 1600
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Would that not be similar to saying:
int *foo;
int bar;
(int *)bar=foo; It's similar to doing:
bar = (int)foo;
Is it, though?
As I said, I don't use that method of calling swis so I'm not familiar with how it works - but I was under the impression that (to use your example) in:
e = _swix(OS_ScreenMode, _IN(0) | _OUT(1), 1, (int)mode_block);
You were telling it to put whatever is in r1 into mode_block - but you were casting that variable. Surely, that's equivalent to putting the cast on the LHS of the equals in a bog standard assignment - ie like (int) mode_block=r.r[1]; - which is just plain wrong.
Of course, sorted now - but if you're insisting that what you were doing was legal, and equivalent to bar = (int)foo; then I would just like to point one little thing to you.
And that thing is this:
bar=(int) foo; works
Your call to _swix in its original form didn't.  |
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Acorn Arcade forums: Programming: OS_ScreenMode problem |
