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Incrementing Pointers

ziplux · 2000-05-01T20:51:59

Hello. I''m having a little trouble understanding pointers, I''ve been told before that I should "increment a pointer," but I don''t really understand what that means. I *think* that this: buffer[x * (y+pitch)] = 5; is the same as: buffer += x * (y+pitch); buffer = 5; Am I correct in assuming this? If so, I don''t understand how the complier can know when you''re advancing a pointer and when you''re setting it to a value. Sorry if this makes absolutely no sense, but maybe someone can help me, I''m starting to confuse myself . Thanks in advance. Visit our web site: Asylum Entertainment

General and Gameplay Programming Programming

Started by ziplux April 28, 2000 09:37 PM

34 comments, last by ziplux 23 years, 11 months ago

adammil

122

May 01, 2000 06:07 PM

Of course I''m sure!

Did you run it?
It works...

adamm@san.rr.com

adamm@san.rr.com

ziplux

122

Author

May 01, 2000 06:44 PM

yeah, I compiled it and it did the same thing it did before I sent it to you. here''s the code you sent to me:

void Blend16(int sx,int sy, int width, int height, int dx, int dy, int alpha, int slPitch16, int dlPitch16, USHORT colorkey, USHORT* svidbuffer, USHORT* dvidbuffer, int pixel_format)	{	// To Do:  Rewrite this function to work with 5.5.5 cards	int index_x, index_y;	int dindex, sindex;	UCHAR sred,sgreen,sblue,dred,dgreen,dblue,fred,fgreen,fblue;/*	for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{			if((svidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))				{				dindex = index_x + dx + dlPitch16 * (index_y + dy);				sindex = index_x + sx + slPitch16 * (index_y + sy);				sred = (((svidbuffer[sindex] >> 11) & 0x1F));				sgreen = (((svidbuffer[sindex] >> 5) & 0x3F));				sblue = ((svidbuffer[sindex]) & 0x1F);								dred = (((dvidbuffer[dindex] >> 11) & 0x1F));				dgreen = (((dvidbuffer[dindex] >> 5) & 0x3F));				dblue = ((dvidbuffer[dindex]) & 0x1F);				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				dvidbuffer[dindex] = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		}*/		dindex = dx + dlPitch16 * dy;		sindex = sx + slPitch16 * sy;		svidbuffer += sindex;		dvidbuffer += dindex;		for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{				if((*(svidbuffer + index_x) != colorkey))				{								sred = (*(svidbuffer + index_x) >> 11) & 0x1F;				sgreen = (*(svidbuffer + index_x) >> 5) & 0x3F;				sblue = *(svidbuffer + index_x) & 0x1F;								dred = (*(dvidbuffer + index_x) >> 11) & 0x1F;				dgreen = (*(dvidbuffer + index_x) >> 5) & 0x3F;				dblue = *(dvidbuffer + index_x) & 0x1F;				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				*(dvidbuffer + index_x) = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		svidbuffer += slPitch16;		dvidbuffer += dlPitch16;		}	}

and before you changed it:

void Blend16(int sx,int sy, int width, int height, int dx, int dy, int alpha, int slPitch16, int dlPitch16, USHORT colorkey, USHORT* svidbuffer, USHORT* dvidbuffer, int pixel_format)	{	// To Do:  Rewrite this function to work with 5.5.5 cards	int index_x, index_y;	int dindex, sindex;	UCHAR sred,sgreen,sblue,dred,dgreen,dblue,fred,fgreen,fblue;/*	for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{			if((svidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))				{				dindex = index_x + dx + dlPitch16 * (index_y + dy);				sindex = index_x + sx + slPitch16 * (index_y + sy);				sred = (((svidbuffer[sindex] >> 11) & 0x1F));				sgreen = (((svidbuffer[sindex] >> 5) & 0x3F));				sblue = ((svidbuffer[sindex]) & 0x1F);								dred = (((dvidbuffer[dindex] >> 11) & 0x1F));				dgreen = (((dvidbuffer[dindex] >> 5) & 0x3F));				dblue = ((dvidbuffer[dindex]) & 0x1F);				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				dvidbuffer[dindex] = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		}*/		dindex = dx + dlPitch16 * dy;		sindex = sx + slPitch16 * sy;		svidbuffer += sindex;		dvidbuffer += dindex;		for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{				if((*(dvidbuffer + index_x) != colorkey))				{								sred = (*(svidbuffer + index_x) >> 11) & 0x1F;				sgreen = (*(svidbuffer + index_x) >> 5) & 0x3F;				sblue = *(svidbuffer + index_x) & 0x1F;								dred = (*(dvidbuffer + index_x) >> 11) & 0x1F;				dgreen = (*(dvidbuffer + index_x) >> 5) & 0x3F;				dblue = *(dvidbuffer + index_x) & 0x1F;				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				*(dvidbuffer + index_x) = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		svidbuffer += slPitch16;		dvidbuffer += dlPitch16;		}	}

These are both the same, right?

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ziplux

122

Author

May 01, 2000 06:44 PM

yeah, I compiled it and it did the same thing it did before I sent it to you. here''s the code you sent to me:

void Blend16(int sx,int sy, int width, int height, int dx, int dy, int alpha, int slPitch16, int dlPitch16, USHORT colorkey, USHORT* svidbuffer, USHORT* dvidbuffer, int pixel_format)	{	// To Do:  Rewrite this function to work with 5.5.5 cards	int index_x, index_y;	int dindex, sindex;	UCHAR sred,sgreen,sblue,dred,dgreen,dblue,fred,fgreen,fblue;/*	for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{			if((svidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))				{				dindex = index_x + dx + dlPitch16 * (index_y + dy);				sindex = index_x + sx + slPitch16 * (index_y + sy);				sred = (((svidbuffer[sindex] >> 11) & 0x1F));				sgreen = (((svidbuffer[sindex] >> 5) & 0x3F));				sblue = ((svidbuffer[sindex]) & 0x1F);								dred = (((dvidbuffer[dindex] >> 11) & 0x1F));				dgreen = (((dvidbuffer[dindex] >> 5) & 0x3F));				dblue = ((dvidbuffer[dindex]) & 0x1F);				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				dvidbuffer[dindex] = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		}*/		dindex = dx + dlPitch16 * dy;		sindex = sx + slPitch16 * sy;		svidbuffer += sindex;		dvidbuffer += dindex;		for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{				if((*(svidbuffer + index_x) != colorkey))				{								sred = (*(svidbuffer + index_x) >> 11) & 0x1F;				sgreen = (*(svidbuffer + index_x) >> 5) & 0x3F;				sblue = *(svidbuffer + index_x) & 0x1F;								dred = (*(dvidbuffer + index_x) >> 11) & 0x1F;				dgreen = (*(dvidbuffer + index_x) >> 5) & 0x3F;				dblue = *(dvidbuffer + index_x) & 0x1F;				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				*(dvidbuffer + index_x) = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		svidbuffer += slPitch16;		dvidbuffer += dlPitch16;		}	}

and before you changed it:

void Blend16(int sx,int sy, int width, int height, int dx, int dy, int alpha, int slPitch16, int dlPitch16, USHORT colorkey, USHORT* svidbuffer, USHORT* dvidbuffer, int pixel_format)	{	// To Do:  Rewrite this function to work with 5.5.5 cards	int index_x, index_y;	int dindex, sindex;	UCHAR sred,sgreen,sblue,dred,dgreen,dblue,fred,fgreen,fblue;/*	for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{			if((svidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))				{				dindex = index_x + dx + dlPitch16 * (index_y + dy);				sindex = index_x + sx + slPitch16 * (index_y + sy);				sred = (((svidbuffer[sindex] >> 11) & 0x1F));				sgreen = (((svidbuffer[sindex] >> 5) & 0x3F));				sblue = ((svidbuffer[sindex]) & 0x1F);								dred = (((dvidbuffer[dindex] >> 11) & 0x1F));				dgreen = (((dvidbuffer[dindex] >> 5) & 0x3F));				dblue = ((dvidbuffer[dindex]) & 0x1F);				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				dvidbuffer[dindex] = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		}*/		dindex = dx + dlPitch16 * dy;		sindex = sx + slPitch16 * sy;		svidbuffer += sindex;		dvidbuffer += dindex;		for (index_y = 0; index_y < height; index_y++)		{		for (index_x = 0; index_x < width; index_x++)			{				if((*(dvidbuffer + index_x) != colorkey))				{								sred = (*(svidbuffer + index_x) >> 11) & 0x1F;				sgreen = (*(svidbuffer + index_x) >> 5) & 0x3F;				sblue = *(svidbuffer + index_x) & 0x1F;								dred = (*(dvidbuffer + index_x) >> 11) & 0x1F;				dgreen = (*(dvidbuffer + index_x) >> 5) & 0x3F;				dblue = *(dvidbuffer + index_x) & 0x1F;				fred = ((l_Alpha[alpha][sred] - l_Alpha[alpha][dred])) + dred;  // same as (alpha * sred - alpha * dred) + dred				fgreen = ((l_Alpha[alpha][sgreen] - l_Alpha[alpha][dgreen])) + dgreen;				fblue = ((l_Alpha[alpha][sblue] - l_Alpha[alpha][dblue])) + dblue;				*(dvidbuffer + index_x) = RGB16(fred << 3,fgreen << 2,fblue << 3);  // scale up the values				}			}		svidbuffer += slPitch16;		dvidbuffer += dlPitch16;		}	}

These are both the same, right?
(BTW I''m 13 years old)

Visit our web site:
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My Geekcode: "GCS d s: a14 C++$ P+(++) L+ E-- W+++$ K- w++(+++) O---- M-- Y-- PGP- t XR- tv+ b++ DI+(+++) D- G e* h!"Decode my geekcode!Geekcode.com
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adammil

122

May 01, 2000 06:47 PM

actually in the file you sent me, you were checking the key against the wrong surface, like this

if((dvidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))

i merely changed it to

if((svidbuffer[index_x + sx + slPitch16 * (index_y + sy)] != colorkey))

and that''s why it was the exact same size

And I''m pretty impressed.. you''re making some pretty cool stuff for 13

adamm@san.rr.com

adammil

122

May 01, 2000 07:48 PM

hmm check your mail again

adamm@san.rr.com

adamm@san.rr.com

ziplux

122

Author

May 01, 2000 08:51 PM

I just got your email. I was looking the code over, but I don''t have time to fix it right now, I''ve got homework :-( But I''ll try tomorrow, and post here again.

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