Having problems moving Snake in Qt - c++

Question

I am doing my very first snake game with Qt creator and I have been stuck for a long time in one single problem. I am using QGraphicsPixmapItem in QGraphicsScene.
Snake head should be different than other body. Now I need to delete all items from scene to draw snake new position to get it work, but I think it's not right way to code it.
How I suppose to update the snake without need delete QGraphicsPixmapItems all the time?
header
struct Point{
int x;
int y;
};
std::vector<Point> snakecore_;
QGraphicsPixmapItem* head_ = nullptr;
QGraphicsPixmapItem* core_ = nullptr;
cpp
delete head_
for(unsigned int i = 0; i < snakecore_.size(); ++i){
if(i == 0){
head_ = scene_.addPixmap(red_);
head_->setPos(snakecore_[i].x, snakecore_[i].y);
}
//Add rest of the snake
}

Answer 1

Moving a snake is quite simple: move the head in the desired direction. Then, move each part to the position of the previous part.
Use a QGraphicsGroupItem to create your snake, it will be simpler to handle the parts.
For example:
class Snake: public QGraphicsItemGroup
{
public:
enum Direction
{
Left,
Right
};
Snake(QGraphicsItem* parent=nullptr): QGraphicsItemGroup(parent), partCount(10)
{
int const partCount = 10;
for( int i = 0; i != partCount; ++i)
{
QGraphicsRectItem* part = new QGraphicsRectItem(QRectF(0, 0, 10, 10), this);
part->setPos((partCount - i) * 10, 0); // Create a snake from left to right
parts << part;
}
}
void move(Direction direction)
{
QPointF const offset = getOffset(direction);
QPointF previousPartPosition = parts.first()->pos();
parts.first()->setPos(parts.first()->pos() + offset);
for( int i = 1; i != partCount; ++i)
{
QGraphicsRectItem* part = parts.at(i);
QPointF const partPosition = part->pos();
part->setPos(previousPartPosition);
previousPartPosition = partPosition;
}
}
QPointF getOffset(Direction direction)
{
switch (direction) {
case Right:
return QPointF(10, 0);
case Left:
return QPointF(-10, 0);
}
}
private:
QList<QGraphicsRectItem*> parts;
int partCount;
};

Answer 2

Your question isn't completely clear, but you don't need to remove the item(s) from the scene to move a graphic item. Just set a new position on each item. They'll move and redraw in their new locations automatically.
Create the head and the body items initially (which you must already be doing), and then you don't need the "delete head_", nor the addPixmap. Just set the positions.