I need help with some coordinates things

Code:

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        //set up rectangle for filling
        RECT rcFill;
        SetRect(&rcFill,ptLastPosition[0].x,ptLastPosition[0].y,ptLastPosition[0].x+gdicBall.GetWidth(),ptLastPosition[0].y+gdicBall.GetHeight());

        //set up a ddbltfx
        DDBLTFX ddbltfx;
        memset(&ddbltfx,0,sizeof(DDBLTFX));
        ddbltfx.dwSize=sizeof(DDBLTFX);

        //set up a color fill of black
        ddbltfx.dwFillColor=0;

        //blt the color fill to the back buffer
        lpddsBack->Blt(&rcFill,NULL,NULL,DDBLT_WAIT | DDBLT_COLORFILL, &ddbltfx);

        //set up source and destination rects for blitting the ball
        RECT rcSrc;
        RECT rcDst;

        SetRect(&rcSrc,0,0,gdicBall.GetWidth(),gdicBall.GetHeight());
        CopyRect(&rcDst,&rcSrc);
        OffsetRect(&rcDst,ptBallPosition.x,ptBallPosition.y);


        /*        ptBallPosition.x=0;//remember that this initialized the
        ptBallPosition.y=0;    //position of the ball and all that.
        ptLastPosition[0].x=0;
        ptLastPosition[0].y=0;
        ptLastPosition[1].x=0;
        ptLastPosition[1].y=0;

        ptBallVelocity.x=16;
        ptBallVelocity.y=8;*/
        //blit the ball
        lpddsBack->Blt(&rcDst,lpddsBall,&rcSrc,DDBLT_WAIT, NULL);//don't really need a source

        //copy current position of ball to old position
        ptLastPosition[0]=ptLastPosition[1];
        ptLastPosition[1]=ptBallPosition;

        //move the ball
        ptBallPosition.x+=ptBallVelocity.x;
        ptBallPosition.y+=ptBallVelocity.y;

        //bounds checking
        //left side
        if(ptBallPosition.x<=0) ptBallVelocity.x=abs(ptBallVelocity.x);
        //top side
        if(ptBallPosition.y<=0) ptBallVelocity.y=abs(ptBallVelocity.y);
        //right side
        if(ptBallPosition.x>=(int)dwDisplayWidth-gdicBall.GetWidth()) ptBallVelocity.x=-abs(ptBallVelocity.x);
        //bottom side
        if(ptBallPosition.y>=(int)dwDisplayHeight-gdicBall.GetHeight()) ptBallVelocity.y=-abs(ptBallVelocity.y);

        //flip surfaces
        lpddsPrime->Flip(NULL,DDFLIP_WAIT);

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I don't really understand that part that is in bold.

When you do this

ptLastPosition[1]=ptBallPosition;


and you don't specify what happens wheter it's ptBallPosition.x or ptBallposition.y what happens?

what is ptLastPosition declared as?

my guess that the entire (struct/class) is copied hence, after

ptLastPosition[1]=ptBallPosition;

ptLastPosition[1]'s 'x' and 'y' 's values should equal that of ptBallPosition's.

//position of the ball
POINT ptBallPosition;
POINT ptLastPosition[2];
//velocity of the ball
POINT ptBallVelocity;

elchulo,
This example is where you have to blit over the last 2 positions of the ball. You are copying the entire struct over. It's the same as if you would have done:

Code:

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ptTwo.x=ptOne.x;
ptTwo.y=ptOne.y;

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just with less typing.. :)

Sorry but is this ptLastPosition[1] like a temperary array? That we use just to transfer the data?

Ok my last ramble for the night, but if
ptLastPosition[0]=ptLastPosition[1];
ptLastPosition[1]=ptBallPosition;

and ptLastPosition[1] is equal to zero, then when we call offrect on the second "round" offrect is not going to move the ball anywhere and this would cause the ball to be blitted twice before it actually moves, by means of offrect or am I wrong? Please help!!!!!!!1

im not exactly sure what yer asking

but if you mean blitting over the balls last two positions before its even originally drawn or moved then yes you would be wasting two blits.

Quote:

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Originally posted by no-one
im not exactly sure what yer asking

but if you mean blitting over the balls last two positions before its even originally drawn or moved then yes you would be wasting two blits.

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Yeah that's about it, Thanks :D

oh BTW that was me from school, didn't feel like signing in, because sometimes I forget and stay signed on!!!!!! Imagine someone posting crap under my name!!!!!?????