Question

Here is my code that checks the type of tile. If its an inclined tile it then updates the
position of the character. As demonstrated in the photo my character does not move along the slope. What am I doing wrong?

bool Entity::PosValidTile(Tile* Tile, int tileX, int tileY)
{
    if(Tile->TypeID == TILE_TYPE_ANGLEUP)
    {
        int Slope, Intercept;
        int newY;

        Vector P1,P2;
        P1.X = tileX; P1.Y = tileY + TILE_SIZE;
        P2.X = tileX + TILE_SIZE; P2.Y = tileY;


        if(X + (Width/2) > tileX)
        {
            Slope = -(P2.Y- P1.Y) / (P2.X - P1.X);

            Intercept = Slope * (-P1.X + P1.Y);

            newY = Slope * ((X + Width/2) + Intercept);

            Y = (newY - Height);

            return true;
        }
    }
}

The dimensions of the character are 48 X 96; which are Width and Height respectively. His origin like the tile, is at the upper left corner.

Here is how that function is used

bool Entity::PosValid(int NewX, int NewY)
{

bool Return = true;

int StartX  = (NewX + Col_X) / TILE_SIZE;
int StartY  = (NewY + Col_Y) / TILE_SIZE;

int EndX    = ((NewX + Col_X) + Width - Col_Width - 1)      / TILE_SIZE;
int EndY    = ((NewY + Col_Y) + Height - Col_Height - 1)    / TILE_SIZE;

if(Flags & ENTITY_FLAG_IGNOREMAP)
{
}else
{
    for(int iY = StartY; iY <= EndY;iY++)
    {
        for(int iX = StartX;iX <= EndX;iX++)
        {
            Tile* Tile = Area::AreaControl.GetTile(iX * TILE_SIZE, iY * TILE_SIZE);

            int atileY = iY * TILE_SIZE;
            int atileX = iX * TILE_SIZE;

            if(PosValidTile(Tile,atileX,atileY) == false)
            {
                Return = false;
            }
        }
    }
}

if(Flags & ENTITY_FLAG_MAPONLY)
{
}else
{
    for(int i = 0;i < (int)EntityList.size();i++)
    {
        if(PosValidEntity(EntityList[i], NewX, NewY) == false)
        {
            Return = false;
        }
    }
}

return Return;
}

The function that calls the previous one is my OnMove function.

void Entity::OnMove(float MoveX, float MoveY)
{
if(MoveX == 0 && MoveY == 0) return;

double NewX = 0;
double NewY = 0;

CanJump = false;

MoveX *= Time::TimeControl.GetDeltaTime();
MoveY *= Time::TimeControl.GetDeltaTime();

if(MoveX != 0)
{
    if(MoveX >= 0)  NewX =  Time::TimeControl.GetDeltaTime();
    else            NewX = -Time::TimeControl.GetDeltaTime();
}

if(MoveY != 0)
{
    if(MoveY >= 0)  NewY =  Time::TimeControl.GetDeltaTime();
    else            NewY = -Time::TimeControl.GetDeltaTime();
}

while(true)
{
    if(Flags & ENTITY_FLAG_GHOST)
    {
        PosValid((float)(X + NewX), (float)(Y + NewY));

        X += (float)NewX;
        Y += (float)NewY;
    }else
    {
        if(PosValid((float)(X + NewX), (int)(Y)))
        {
            X += (float)NewX;
        }else
        {
            SpeedX = 0;
        }

        if(PosValid((float)(X), (float)(Y + NewY)))
        {
            Y += (float)NewY;

        }else
        {
            if(MoveY > 0)
            {
                CanJump = true;
            }
            SpeedY = 0;
        }
    }

    MoveX += (float)-NewX;
    MoveY += (float)-NewY;

    if(NewX > 0 && MoveX <= 0) NewX = 0;
    if(NewX < 0 && MoveX >= 0) NewX = 0;

    if(NewY > 0 && MoveY <= 0) NewY = 0;
    if(NewY < 0 && MoveY >= 0) NewY = 0;

    if(MoveX == 0) NewX = 0;
    if(MoveY == 0) NewY = 0;

    if(MoveX == 0 && MoveY  == 0)   break;
    if(NewX  == 0 && NewY   == 0)   break;
}
}

This function is then called in the main Loop Like so
OnMove(SpeedX,SpeedY);
The speeds are calculated as fallows

    SpeedX += AccelX * Time::TimeControl.GetDeltaTime();
    SpeedY += AccelY * Time::TimeControl.GetDeltaTime();

Answer 1

I’m giving an “answer” but it probably better fit as a comment… a few points:

• First question, what’s happening in the debugger? Do you even get in the if?
• I don’t see a mention of delta time anywhere, it should be used to get smooth time dependent movement (not frame dependent)
• PosValidTile doesn’t say much about what the function does… you seem to modify your Entity Y value but not the X? if you don’t move horizontally against the slope, it’s normal that you don’t go up either!
• TILE_TYPE_ANGLEUP doesn’t make much sense to me, as its “angle” is “down” if your character turns and goes from right to left
• I guess character movement is determined elsewhere? The heading of your character should be taken into account to know on which side of the slope you’re going (your “next” X, which doesn’t seem to be computed here)
• Is the function here incomplete? not all paths return a value

Edit: You posted new code where you use PosValidEntity using NewX and NewY – we don’t see where these values are set to, but keep in mind that your PosValidTile seems to modify directly Y, not a “tentative NewY”.

Also, I’m not too sure what your Intercept is supposed to do. Basically you have your Slope and you want to know how many pixels along the X axis you are, multiply the Slope by this relative value and then add the base Y. In your case Slope is always TILE_SIZE / TILE_SIZE -> 1 so finding your new Y should be as easy as something like – if it’s not always 1, simply multiply the relative X by that slope

Y = X + (Width/2) - tileX + tileY;

You take the X position of your character, add the Half Width and the remove the base X value of the tile, this gives you how far along the X axis you are on the slope. Since your slope is always 1, you are as far along the Y axis as you are on the X axis, so if you add (or subtract in your case because I think higher values mean lower on the screen in your coordinates?) this value to your base Y you should get your Y value.