Xref:	news2.mv.net comp.os.msdos.djgpp:8149
From:	"Mark Gilbert" <mark DOT gilbert AT pop3 DOT hiway DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Assembler problem
Date:	1 Sep 1996 12:48:12 GMT
Organization:	UUNet PIPEX server (post doesn't reflect views of UUNet PIPEX)
Lines:	73
Message-ID:	<01bb9803$2adbeac0$89fa82c1@hiway.co.uk.hiway.co.uk>
NNTP-Posting-Host:	ak137.du.pipex.com
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I have a limited understanding of assembler (so please don't shout at me).
This is an in-line asm routine from a platform game I'm making . . .

      for(n=0;n<200;n++)
                {
                      n3=((n+yoff) << 12) + ((n+yoff) << 10)+(n2-100);
                      asm(
                                "push %eax\n\t"
                                "push %ebx\n\t"
                                "push %ecx\n\t"
                                "push %edx\n\t"
                                "push %edi\n\t"
                                "push %esi\n\t"
                                "movl _imgbuffer, %esi\n\t"
                                "addl _n3, %esi\n\t"
                                "movl _doublebuffer, %edi\n\t"
                                "addl _n1, %edi\n\t"
                                "movl 0, %ecx\n\t" 
                                "movl $0, %eax\n\t"
                                "movl $320, %ebx\n\t"
                                "movb $119, %edx\n\t"
                                "lint:\n\t"
                                "movb (%esi), %edx\n\t"
                                "cmpb 0, %edx\n\t"
                                "jne mints\n\t"     
                                "mintsa:\n\t"
                                "addl $1, %eax\n\t"
                                "addl $1, %esi\n\t"
                                "addl $1, %edi\n\t"
                                "cmp %ebx, %eax\n\t"
                                "jne lint\n\t"
                                "pop %esi\n\t"
                                "pop %edi\n\t"
                                "pop %ecx\n\t"
                                "pop %edx\n\t"
                                "pop %ebx\n\t"
                                "pop %eax\n\t"
                                "mints:\n\t"
                                "movb %edx, (%edi)\n\t"
                                "jne mintsa\n\t"
                      );       
			n1+=320;
                }


The level is a huge image (imgbuffer) that is well about 5120x600, whilst
the screen mode I'm using is standard 320x200 with 256 colours. This
routine copies a 320x200 segment from the imgbuffer to the doublebuffer
(64000 chars) whilst ignoring colour 119 to allow the background to show
through.

This routine is a little faster than the C equivalent I made. But it has
some major, major problems.

In Windows95 8 out of ten times I run it works perfectly but occasionally
when the games loads the colour it ignores changes for the hole session. I
simply don't understand this one at all. My C equivalent didn't do this.

When run in DOS via CWSDPMI it bombs out and gives a page fault as soon as
it gets to this assembler section. But when run through PMODETSR I don't
get a page fault but instead the bit that the assembler draws is all
corrupt.

I know that there's a lot to look at but could you please help me out.

Forgive me for having labels such as lint.

-- 

Mark Gilbert
mark DOT gilbert AT pop3 DOT hiway DOT co DOT uk
http://ourworld.compuserve.com/homepages/chris_gilbert_10/scissor.htm

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