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Collisions & Physics

MD Engine provides a simple collision & physics system; it's not a fully featured physics engine like Box2D, but good enough for arcade-style platformers, shooters, puzzles, etc.

There are several physics values, local to each actor:

  • Position
  • Velocity X / Y
  • Acceleration X / Y

Also, some are global to the entire game:

  • Maximum Velocity X / Y
  • Deceleration X / Y
  • Acceleration
  • Gravity
  • Jump

You can adjust the global ones on the Global Values settings.

The global acceleration, gravity, and jump values are used automatically for the Platformer Behaviour.

Collision System​

There are three different collision systems available to choose, Simple, Advance (Fast), and Advance (Slow).

The major difference is that on the Advance system, actors can push each other while on the simple they overlap but can't physically move one another.

Actor Overlap Behaviour​

When two actors overlap each other you can adjust how the On Collide scripts are invoked, it can be changed on the Collisions settings.

  • First Time - This option makes the On Collide been called only the first time it happens, and it won't be called again until they stop overlapping.
  • Continuous - This option makes the On Collide been called all frames since it happens until there is no overlap.
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Be aware First Time option may behave the same as Continuous option if both actors are solid and you are using the Advance system.
Due to actors never fully overlapping, they separate and adjust their positions.

Collision Mode​

This is an adjustment that you can enable different ways of calculating the collisions.
You can choose between All Actors, Only On-Screen Actors, and Gridding.

All Actors​

This is the default option, it will work fine for most games that have a reduced amount of actors and small levels.

Only On-Screen Actors​

This is the best option if you have very large levels and a lot of actors spread, this way only actors that are on-screen are checked for collisions.

Gridding​

This is the best options for shooters that feature a lot of bullets and actors, you can adjust the grid sizes, as well as how the objects are gridded to get the best possible performance.

Collision Special Options​

Collision Tiles​

Collision Tiles refers to the export size of the scene collisions information, you can set either 8x8 pixels or 16x16 pixels.
This options helps reduce the amount of RAM used on collision information as well as the ROM size if all your collisions are placed on 16x16px squares.
During build time if you have any square with collision information that is not correct a warning will be printed.

Collision Bias​

Collision bias refers to a small numerical adjustment (or tolerance) used to prevent actors from "sticking," jittering, or tunneling through each other.

Collision Masking​

Collision masking is a technique used in physics simulations to control which actors can collide or interact with each other.

Instead of every actor checking collisions against every other actor (which can be inefficient or undesirable), collision masking lets you define groups that specify which collisions should be considered.

You can assign each actor to a specific group in the actor settings.

After that, you can select if each collision group overlaps another by just clicking the box.

Collision Frequency​

You can adjust the frequency each of the collision groups will be checked.
The options change depending ont he collision mode

All Actors​

The All Actors mode allows you to check how each group is check.
This helps increase the performance without having to change to a different collision mode.

Only On-Screen Actors & Gridding​

These two modes allow you to check how each projectile group is check.
This helps improve the performance of shooters a bit more when using gridding system.