Finding Room for a Shape on a Grid

I'm working on a game where you have an 8x12 grid where each cell is the same size and all the cells are directly next to one another.

You drag around various Tetris-like shapes and place them on the grid in valid locations, a valid location being one where all the cells that the shape will occupy are not occupied by some other shape.

My problem is that I'm not sure how to search the grid space for valid locations. I've been searching for an algorithm that will solve this 开发者_如何学Pythonsort of problem, but I have come up empty handed thus far. It seems like it should be pretty straightforward to detect valid locations, but I have not been able to come to a successful solution.

Any processes, algorithm suggestions, or ideas for how to go about solving this would be extremely helpful. Thanks!

EDIT:

Here is the expected functionality: When the shape is in a valid location, it can be dragged between valid locations freely and follows the mouse pointer. However, when you try to drag the shape into an invalid area (ie movement in the direction specified would place one or more blocks of the shape in invalid locations), it stays in the last valid location.

At this point, when the mouse is in an invalid area, I want to do some "predictive" movement so that if the player moves the mouse cursor near a valid position, the shape then "snaps" into place, say if the valid position is two grid spaces away.

Thanks for your suggestion so far; I hadn't thought of that method!

As described, the algorithm would be quite simple. Arbitrarily choose a starting block on your shape, and try to match it to each open cell of the grid. If "drawing" the shape with the block aligned with the current cell doesn't cause a collision, you've found a valid position.