GML+ includes a number of built-in variables and constants which can be accessed in your own code. These can provide useful information or behaviors that are commonly needed, but have no implementation in vanilla GML.
All built-in variables are provided by the
obj_gmlp object. This object must be present in the current project, but does not need to be added to any rooms to function.
|real||Stores the instance sprite rotation from the previous step, as a value of degrees.|
|real||Stores the instance sprite X scale from the previous step, as a value of degrees.|
|real||Stores the instance sprite Y scale from the previous step, as a value of degrees.|
image_angle should not be confused with
direction. While both are built-in to each instance,
image_angle modifies the sprite while
direction modifies movement.
|real||Stores the current horizontal mouse speed, as a value of pixels.|
|real||Stores the current vertical mouse speed, as a value of pixels.|
|real||Stores the current directional mouse speed, as a value of pixels.|
|real||Stores the current mouse direction of travel, as a value of degrees.|
|real||Stores the mouse X coordinate upon starting the game. If no mouse is used, -1 will be returned. Like the instance |
|real||Stores the mouse Y coordinate upon starting the game. If no mouse is used, -1 will be returned. Like the instance |
|real||Stores the mouse X coordinate from the previous Step. Like the instance |
|real||Stores the mouse Y coordinate from the previous Step. Like the instance |
|boolean||Shows or hides the mouse, while preserving cursor state and/or sprite. Set to |
GameMaker Studio 2 uses two separate functions for setting different types of cursors. For system cursors, use
window_set_cursor([cursor]). For sprite cursors, use GML+'s
window_set_cursor_sprite([sprite]). Unlike vanilla GML, GML+ will automatically switch the cursor type when either command is used.
|real||Stores the amount of time a single frame should take to render at the current game speed (FPS), as a value of milliseconds.|
|real||Stores the actual time the previous frame took to render, as a value of milliseconds.|
|real||Stores the difference (or delta) between the target and actual frame time, as a multiplier.|
While the use-case for these constants and variables may not be immediately obvious, in reality they're some of the most important properties in your entire project. Much game logic occurs over time, and while it may be tempting to rely on FPS as a unit of time, this will cause a host of problems down the road. FPS-based logic can never run at another framerate without altering its real-world speed--frustrating for users on high-end systems that could run the game faster, and frustrating for low-end users that can't hit the target framerate to begin with.
A better unit of time is the time it took to render the previous frame, or simply
frame_time. Frame time-based logic will always run at the same real-world speed regardless of framerate. This both compensates for lag on low-end systems and allows high-end systems to run to their full potential.
You may have previously heard of this concept referred to as delta time. However, this is a bit of a misnomer. Strictly speaking, delta time is not the previous frame time, but rather the difference between the current frame time and the previous frame time. Though the term is often misused,
frame_delta is nonetheless a very useful property to be aware of. In fact,
frame_delta are like two sides of the same coin, only forming a whole when used together.
Which available time constant or variable you should use in your logic depends on the kind of logic itself. For time-based logic (e.g. clocks, timers, etc.), use
frame_time as a unit of milliseconds. For distance-based logic (e.g. movement, rotation, etc.), use
frame_delta as a multiplier of pixels, degrees, and so forth.
For further explanation of how to implement frame time and delta time in your projects, see the video tutorial below: