Beginner’s Guide to GML: Getting Started with GameMaker Language

Migrating from Drag-and-Drop to GML: A Step-by-Step WorkflowSwitching from Drag-and-Drop (DnD) to GameMaker Language (GML) is a common milestone for GameMaker Studio users who want more control, better performance, and cleaner, scalable projects. This article lays out a practical, step-by-step workflow to help you migrate projects confidently while minimizing bugs and keeping development moving forward.

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Why migrate from Drag-and-Drop to GML?

• Greater flexibility: GML exposes more engine features and allows custom logic not possible with DnD.
• Improved performance: Well-written GML tends to run faster than equivalent DnD code.
• Scalability and maintainability: Text code is easier to refactor, reuse, and version-control.
• Community and learning: Many tutorials, libraries, and examples use GML.

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Preparation: plan before you convert

1. Inventory your project

   • List all objects, events, and scripts that rely on DnD.
   • Identify complex DnD chains (long sequences of actions) and visual scripts that are frequently edited.

2. Set migration goals

   • Full rewrite vs. incremental conversion (recommended: incremental).
   • Prioritize converting core systems first (input, movement, collision, UI).

3. Set up version control & backups

   • Commit current project to Git, or make manual backups.
   • Create a separate branch for migration work.

4. Establish coding standards

   • Decide naming conventions, file organization (scripts vs. object code), and comment style.
   • Consider using functions and scripts to promote reuse.

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Step 1 — Learn GML equivalents for DnD actions

Start by mapping DnD actions to GML functions and constructs. Common pairs:

• Movement: DnD “Set Speed / Direction” -> speed, direction, motion_set, move_towards_point(), vs built-in physics functions.
• Collisions: DnD “If collision with object” -> collision_rectangle(), place_meeting(), instance_place(), event_collision.
• Instance creation: DnD “Create Instance” -> instance_create_layer(x, y, layer, obj).
• Variables: DnD “Set Variable” -> myVar = value; variables are dynamically typed.
• Timers: DnD “Alarm” actions -> alarm[n] and alarm[n] event code.
• Sounds: DnD “Play Sound” -> audio_play_sound(sound, priority, loop).
• Room transitions: DnD “Go to Room” -> room_goto(room_index) or room_goto_next().

Refer to the GameMaker manual for specific function signatures and any engine-version differences.

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Step 2 — Start small: convert a single object

Choose a simple, self-contained object (for example, a pickup or a button) and convert its DnD events into GML.

• Open the object’s events and for each DnD action, write equivalent GML in the corresponding event.
• Replace chained DnD actions with clear, commented code blocks.
• Test the object in-game and fix any immediate issues.

Example: converting a coin pickup

• DnD: On collision with player -> Play sound; Increase score; Destroy instance.
• GML (in Collision event with obj_player):

  
  audio_play_sound(snd_pickup, 1, false); global.score += 10; instance_destroy(); 

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Step 3 — Convert systems, not just objects

After practicing with single objects, tackle whole systems: input handling, player movement, enemy AI, UI, and physics. Converting systems yields more predictable behavior and easier debugging.

• Centralize input: move keyboard/mouse handling into a controller object or the player’s Step event.
• Movement & physics: replace multiple DnD motion actions with single, coherent GML routines (use friction, acceleration variables).
• Collision handling: prefer place_meeting()/instance_place() checks and collision events for deterministic behavior.
• UI and HUD: separate drawing logic into Draw GUI event, using draw_text_ext(), draw_sprite(), and viewports.

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Step 4 — Create utility scripts and libraries

To reduce duplicated code and speed conversion, write scripts (GML functions) for common tasks.

Examples:

• script_get_direction_to_point(x, y)
• script_spawn_enemy(type, x, y)
• script_apply_damage(target, amount, source)

Organize scripts into folders (Player, Enemies, UI, Utilities) and document expected parameters.

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Step 5 — Maintain game behavior: regression testing

After converting parts, run systematic tests to ensure behavior matches the DnD version.

• Keep a “reference build” (a copy of the DnD project) for comparison.
• Create test rooms or automated checks: confirm movement speeds, collision ranges, timings, and UI updates.
• Log discrepancies and address them in small, focused commits.

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Step 6 — Optimize and refactor

Once functional parity is reached, refine the code:

• Replace repetitive code with functions.
• Use arrays/structs for grouped data (e.g., stats, inventories).
• Profile performance: check heavy loops and frequent events; move costly computations to less frequent events or coroutines.
• Consider Data Structures (maps, lists) for complex state.

Example: using a struct for a player:

player = {     hp: 100,     speed: 4,     equip: ds_map_create() }; 

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Step 7 — Final sweep and cleanup

• Remove unused DnD objects/events.
• Rename scripts and objects for clarity.
• Update room instances to use new object behaviors if you created new objects.
• Ensure build settings (export targets, asset paths) are correct.

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Common pitfalls and solutions

• Timing differences: DnD actions sometimes execute in chained batches; replicate exact timing with alarms or step-order logic.
• Scope and variable naming: DnD “Variable” actions may use different scopes (instance vs. global). Be explicit: use global.var or instance.var as needed.
• Events order: Understand GameMaker’s event order to preserve event interactions (Begin Step, Step, End Step, Draw).
• Unintended persistence: DnD-created persistent objects may behave differently once restructured—check object persistence flags.

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Example migration checklist (short)

• [ ] Backup & version control
• [ ] Inventory DnD usage
• [ ] Convert simple objects
• [ ] Convert core systems
• [ ] Create utility scripts
• [ ] Regression test
• [ ] Optimize
• [ ] Clean up

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Resources

• GameMaker manual (refer to functions and event behaviors)
• Community forums and example GML scripts
• Existing open-source GameMaker projects for reference

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Migrating from DnD to GML is an investment: the upfront cost pays off with cleaner, faster, and more flexible projects. Take it step-by-step, test frequently, and lean on utility scripts to keep the work manageable.