#Stencyl: Zerg terrain infection

Part 1: Creating building, making building follow mouse, placing building

Topics:

• Choosing building on keyboard key
• Cancel chosen building
• Make building follow the mouse
• Placing building
  
  

Behaviors used in part I

Behavior:

• main scene behavior (scene behavior)
  • when created
  • when e pressed
  • when r pressed
  • on mouse-click
  • when d pressed

Main variables:

• building_active - Boolean; if there is a building following the mouse
• tile_size - Number; size of tiles in pixels
• active_building - Actor; Stores picked building

For tiles and building actors we change Physics->General->What kind of Actor Type? to <cannot move> and Physics->Advanced -> Actor Mode to <Simple>.

In when create we declare tile size(<tile_size>) in pixels. We declare <building_active> to false. <building_active> says if we picked building. We create <building_list> matrix that will be used in checking if there is a place for placing picked building.

Choosing building on keyboard key

-> <when e pressed>

We check if there is no building picked by checking (if (not(<building_active>) ) ). If this is true we create building. We set <building_active> to <true> since we picked building. We set <active_building> to <last created actor>. We move <last created actor> so that it has center on the mouse position.

I assume that all created actors this way have width and height equal to multiplied tiles. Implementation for second building is pretty much the same expect it is <when r pressed> event.

Cancel chosen building

-> <when d pressed>

If player has made a mistake and picked the wrong type of building we allow them to cancel their choice. We check if there exists picked actor and if it's true we kill it and mark this fact by setting <building_active> to <false>.

Make building follow the mouse

-> <on update event>

First If <building_active> checks if building exists. If yes we set building so it's center is at the mouse position.

Then we check 4 ifs in order to prevent building from leaving the screen. If x < 0 and if y < 0 are obvious the other pair might seem strange(explanation on picture below).

The second pair of <set x> and <set y> snaps the position of building to the grid.

 

Picture shows the building in position to most right and it is last position acceptable in that direction(yellow). If the building was anymore to the right it should be limited to that position since otherwise some part of actor would leave screen.

Snapping to grid means that we should change the current position of actor(purple) to node of the grid(black).

Code analysis for x direction. In this project we set <tile_size> to 16. For x = 8; x/16 = 0.5. Since we apply floor -> floor (0.5) = 0. This means that purple point will be moved to the tile number 0 counting from the left. In order to update position of actor we need to return to pixel values so we multiply it number of tile by <tile_size> and we get x-position = 0 (value in pixels).

The floor function is nice because you know that coordinates of nodes to the right and bottom from checked node are limits of how far a purple point can get from the checked node point while still being snapped to it. It's much easier than using round function.

Placing building

-><when mouse was pressed>

First If <building_active> checks if there is a building picked. If yes we ask if there are no other building on space where we are about to place building by triggering <building_check> (more details in Part II). If that's ok we place building. Since the building is placed and we don't want it to follow mouse anymore we set <building_active> to <false>. Then we trigger <placed_on_map> to force building to do all the work associated with its arrival (Part II).

To choose other part follow the link:

http://t4upl.blogspot.com/2015/07/stencylzerg-terrain-infection.html