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Sphet

DirectX, Home made Bltters, Assembly

2 posts in this topic

Hey.. I''m trying to implement some special blts for my project and have realized that it should be done in assembly. I don''t have much experience with it, and was wondering if anyone could point me to a good tutorial on pentium-era assembly coding. I''m using Visual C++ 6.0, and have, of course, access to the inline assembly using __asm {}. I''ve done some tests with it an the blitting speed isn''t too slow, except I am having some problems. My function is like this: ERROR_Type BLT_BltTestOne(Sprite *sprite) { __asm { MOV EAX, sprite->data } } I get errors, no double because the assembler can''t understand the -> pointer. How do I use pointers in inline assembly? Also, what are the speed advantages to calling out to a pure assembly OBJ instead of an inline call? Any help or samples would be appreciated. I would rather keep to directX blitters, but I need to do some specialized transparencies and such..
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You should stick the indirection into a temporary variable, and reference the variable from the inline assembly. Otherwise you have to dereference your sprite in assembly. yeech.

Compiling into a asm obj files has the hit of needing to cross the function call boundary. i.e. you need to do the stack stuff, not to mention a propable cache miss for non-local code jump. inline for that reason is faster if used properly.
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Ok. Lets say your Sprite struct looks like this:

typedef struct
{
DWORD Sprite_Width,Sprite_Height;
DWORD Xpos,Ypos;
DWORD *Data;
} Sprite;

Now, in this example, I''m assuming your sprite data is
32-bits.

Then in inline-asm:

========================================== SNIP ============

ERROR_Type BLT_BltTestOne(Sprite *sprite)
{
__asm
{
// point esi to your sprite
MOV esi,sprite

// to get the xpos, you add 8 to the ESI pointer
// because each member of the struct is a DWORD which
// is 4 bytes.
MOV eax,[esi+8]

// to access the sprite data, you would do this
MOV edi,[esi+32]
}
}

=== SNIP ===================================================

That should do it and VC will not complain.




~-------------------------------------------------------~
Fred Di Sano
System Programmer - Artech Studios (Ottawa.CA)
~-------------------------------------------------------~
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