Agent Skills: Makepad 2.0 DSL Syntax Skill

Makepad 2.0 DSL Syntax Skill

Overview

Makepad 2.0 replaced the compile-time live_design! macro with the runtime script_mod! macro, powered by the Splash scripting language. This skill covers the complete DSL syntax, property system, registration patterns, and common pitfalls.

Key Syntax Rules

Property Assignment: Colon, NOT Equals

key: value          // CORRECT - colon syntax
key = value         // WRONG - old 1.x syntax, no longer works

Properties are whitespace/newline separated. No commas between siblings.

View{
    width: Fill
    height: Fit
    flow: Down
    spacing: 10
    padding: 15
}

Named Instances: := Operator

Use := to create addressable, named widget instances:

my_button := Button{ text: "Click me" }
title := Label{ text: "Hello" }

Named instances are:

• Addressable from Rust code via id!(my_button) or ids!(my_button)
• Overridable via dot-path syntax: MyTemplate{ title.text: "New text" }
• Stored in the script object's vec (not map)

Regular properties use : and go into map:

width: Fill       // regular property -> map
label := Label{}  // named child -> vec

Merge Operator: +:

The +: operator extends/merges with the parent instead of replacing:

draw_bg +: {
    color: #f00    // Only overrides color, keeps all other draw_bg properties
}

Without +:, you REPLACE the entire property:

draw_bg: { color: #f00 }    // REPLACES all of draw_bg - loses hover, border, etc.
draw_bg +: { color: #f00 }  // MERGES - only changes color, keeps everything else

Dot-Path Shorthand

Dot-path is syntactic sugar for merge:

draw_bg.color: #f00
// is equivalent to:
draw_bg +: { color: #f00 }

draw_text.text_style.font_size: 14
// is equivalent to:
draw_text +: { text_style +: { font_size: 14 } }

Let Bindings: Local Templates

let creates local, reusable templates within a script_mod! block:

let MyCard = RoundedView{
    width: Fill height: Fit
    padding: 16 flow: Down spacing: 8
    draw_bg.color: #2a2a3d
    draw_bg.border_radius: 8.0
    title := Label{ text: "Default Title" draw_text.color: #fff }
    body := Label{ text: "" draw_text.color: #aaa }
}

// Instantiate and override:
MyCard{ title.text: "Card 1" body.text: "Content here" }
MyCard{ title.text: "Card 2" body.text: "More content" }

IMPORTANT: let bindings are LOCAL to the script_mod! block. They cannot be accessed from other script_mod! blocks. To share across modules, store in mod.widgets.*.

Spread Operator: ..

Inherit all properties from another definition:

set_type_default() do #(DrawMyShader::script_shader(vm)){
    ..mod.draw.DrawQuad   // Inherit from DrawQuad
}

Script Module Structure

Basic App Structure

use makepad_widgets::*;

app_main!(App);

script_mod!{
    use mod.prelude.widgets.*

    load_all_resources() do #(App::script_component(vm)){
        ui: Root{
            main_window := Window{
                window.inner_size: vec2(800, 600)
                body +: {
                    // UI content here
                    my_button := Button{ text: "Click" }
                }
            }
        }
    }
}

impl App {
    fn run(vm: &mut ScriptVm) -> Self {
        crate::makepad_widgets::script_mod(vm);  // 1. Register base widgets
        App::from_script_mod(vm, self::script_mod)
    }
}

#[derive(Script, ScriptHook)]
pub struct App {
    #[source] source: ScriptObjectRef,   // REQUIRED for Script-derived structs
    #[live] ui: WidgetRef,
}

impl MatchEvent for App {
    fn handle_actions(&mut self, cx: &mut Cx, actions: &Actions) {
        if self.ui.button(ids!(my_button)).clicked(actions) {
            log!("Button clicked!");
        }
    }
}

impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        self.match_event(cx, event);
        self.ui.handle_event(cx, event, &mut Scope::empty());
    }
}

Widget Definition Module

script_mod!{
    use mod.prelude.widgets_internal.*   // For widget library internals
    use mod.widgets.*                     // Access other registered widgets

    // Step 1: Register the Rust struct as a widget base
    mod.widgets.MyWidgetBase = #(MyWidget::register_widget(vm))

    // Step 2: Create a styled variant with default properties
    mod.widgets.MyWidget = set_type_default() do mod.widgets.MyWidgetBase{
        width: Fill
        height: Fit
        padding: theme.space_2

        draw_bg +: {
            color: theme.color_bg_app
        }
    }
}

Registration Patterns

Widget Registration

For structs that implement the Widget trait:

mod.widgets.MyWidgetBase = #(MyWidget::register_widget(vm))

Rust side:

#[derive(Script, ScriptHook, Widget)]
pub struct MyWidget {
    #[source] source: ScriptObjectRef,  // REQUIRED
    #[walk] walk: Walk,
    #[layout] layout: Layout,
    #[redraw] #[live] draw_bg: DrawQuad,
    #[live] draw_text: DrawText,
    #[rust] my_state: i32,  // Runtime-only, not exposed to script
}

Component Registration

For non-widget structs that need script integration:

mod.widgets.MyComponentBase = #(MyComponent::script_component(vm))

Draw Shader Registration

For custom draw types with shader fields:

set_type_default() do #(DrawMyShader::script_shader(vm)){
    ..mod.draw.DrawQuad   // Inherit from DrawQuad
}

Rust side:

#[derive(Script, ScriptHook)]
#[repr(C)]
pub struct DrawMyShader {
    #[deref] draw_super: DrawQuad,
    #[live] my_param: f32,
}

Setting Type Defaults

mod.widgets.MyWidget = set_type_default() do mod.widgets.MyWidgetBase{
    width: Fill height: Fit
    draw_bg +: { color: theme.color_bg_app }
}

Registration Order (CRITICAL)

Widget modules MUST be registered BEFORE UI modules that use them:

impl App {
    fn run(vm: &mut ScriptVm) -> Self {
        crate::makepad_widgets::script_mod(vm);   // 1. Base widgets FIRST
        crate::my_widgets::script_mod(vm);         // 2. Custom widgets SECOND
        crate::app_ui::script_mod(vm);             // 3. UI using widgets THIRD
        App::from_script_mod(vm, self::script_mod) // 4. App component LAST
    }
}

Multi-Module Aggregation (lib.rs pattern)

pub fn script_mod(vm: &mut ScriptVm) {
    crate::module_a::script_mod(vm);
    crate::module_b::script_mod(vm);
    // ... all widget modules
}

Prelude System

Available Preludes

| Prelude | Use Case | |---------|----------| | mod.prelude.widgets.* | App development - includes all standard widgets | | mod.prelude.widgets_internal.* | Widget library internal development |

Prelude Alias Syntax

mod.prelude.widgets = {
    ..mod.std,            // Spread all of mod.std into scope
    theme:mod.theme,      // Create 'theme' as alias for mod.theme
    draw:mod.draw,        // Create 'draw' as alias for mod.draw
}

Without the alias (mod.theme, without theme:), the module is included but has no accessible name.

Cross-Module Sharing

The mod Object is the ONLY Way to Share

// In widget_module.rs - export to mod.widgets namespace
script_mod!{
    use mod.prelude.widgets_internal.*
    mod.widgets.MyWidget = set_type_default() do mod.widgets.MyWidgetBase{ ... }
}

// In app_ui.rs - import via mod.widgets
script_mod!{
    use mod.prelude.widgets.*
    use mod.widgets.*   // Now MyWidget is in scope
    // ...
    MyWidget{}
}

use crate.module.* does NOT work - the crate. prefix is not available in script_mod.

Runtime Property Updates

Use script_apply_eval! instead of the old apply_over + live!:

// Old system
item.apply_over(cx, live!{ height: (height) });

// New system - use #(expr) for Rust expression interpolation
script_apply_eval!(cx, item, {
    height: #(height)
    draw_bg: { is_even: #(if is_even { 1.0 } else { 0.0 }) }
});

Debug Logging

Use ~expression to log values during script evaluation:

script_mod!{
    ~mod.theme           // Logs the theme object
    ~mod.prelude.widgets // Logs what's in the prelude
    ~some_variable       // Logs a variable's value
}

Common Pitfalls

1. Missing #[source] source: ScriptObjectRef

All Script-derived structs MUST have this field:

#[derive(Script, ScriptHook)]
pub struct MyStruct {
    #[source] source: ScriptObjectRef,  // REQUIRED - will fail without it
    // ...
}

2. Missing height: Fit on Containers

Default height is Fill. In a Fit parent, Fill creates a circular dependency = 0 height = invisible:

// WRONG - invisible!
View{ flow: Down
    Label{ text: "You can't see me" }
}

// CORRECT
View{ height: Fit flow: Down
    Label{ text: "Visible!" }
}

3. Confusing : vs :=

• key: value -- sets a property (stored in map)
• name := Widget{} -- creates a named, addressable child (stored in vec)
• label := Label{ text: "x" } -- named, overridable via Template{ label.text: "y" }
• label: Label{ text: "x" } -- anonymous, NOT addressable, overrides fail silently

4. Forgetting +: Merge Operator

// WRONG - replaces ALL of draw_bg (loses hover, border, animations)
draw_bg: { color: #f00 }

// CORRECT - merges, only changes color
draw_bg +: { color: #f00 }

5. Wrong Theme Access

// WRONG
color: THEME_COLOR_BG     // old 1.x constant syntax
color: (THEME_COLOR_BG)   // old 1.x parenthesized reference

// CORRECT
color: theme.color_bg_app
padding: theme.space_2
font_size: theme.font_size_p

6. Hex Colors Containing 'e' Need #x Prefix

The Rust tokenizer interprets e/E in hex literals as scientific notation exponent:

// WRONG - Rust parse error: "expected at least one digit in exponent"
color: #2ecc71
color: #1e1e2e

// CORRECT - use #x prefix
color: #x2ecc71
color: #x1e1e2e

// Colors without 'e' work fine with plain #
color: #ff4444    // OK
color: #44cc44    // OK

7. pub Keyword Invalid in script_mod

// WRONG
pub mod.widgets.MyWidget = ...

// CORRECT - visibility is controlled by Rust module system
mod.widgets.MyWidget = ...

8. Inset{...} Constructor Syntax for Margins/Padding

// WRONG
margin: { left: 10 }
align: { x: 0.5 y: 0.5 }

// CORRECT - use constructor syntax
margin: Inset{ left: 10 }
align: Align{ x: 0.5 y: 0.5 }
padding: Inset{ top: 5 bottom: 5 left: 10 right: 10 }

// Bare number for uniform values is OK
padding: 15
margin: 0.

9. Draw Shader Struct Field Ordering with #[repr(C)]

Non-instance data (#[rust], non-instance #[live] fields) MUST go BEFORE #[deref]. Only instance fields (shader inputs) go AFTER:

// CORRECT
#[derive(Script, ScriptHook)]
#[repr(C)]
pub struct MyDrawShader {
    #[live] pub svg: Option<ScriptHandleRef>,  // non-instance, BEFORE deref
    #[rust] my_state: bool,                     // non-instance, BEFORE deref
    #[deref] pub draw_super: DrawQuad,          // contains DrawVars + base instances
    #[live] pub tint: Vec4f,                    // instance field, AFTER deref - OK
}

// WRONG - #[rust] after instance fields corrupts GPU buffer
#[derive(Script, ScriptHook)]
#[repr(C)]
pub struct MyDrawShader {
    #[deref] pub draw_super: DrawQuad,
    #[live] pub tint: Vec4f,
    #[rust] my_state: bool,      // BAD: between instance fields
}

10. No Comments Before First Code in script_mod!

Rust proc macro token stream strips comments, which shifts error positions:

// WRONG
script_mod!{
    // This comment shifts error line info
    use mod.prelude.widgets.*
}

// CORRECT - start with real code immediately
script_mod!{
    use mod.prelude.widgets.*
    // Comments after first code are fine
}

Additional Pitfalls

• Cursor values: Use cursor: MouseCursor.Hand not cursor: Hand or cursor: @Hand
• Resource paths: Use crate_resource("self://path") not dep("crate://self/path")
• Texture declarations: Use tex: texture_2d(float) not tex: texture2d
• Shader mod vs modf: Use modf(a, b) for float modulo, NOT mod(a, b)
• Enum defaults: Use default: @off with @ prefix for enum default values
• DefaultNone derive: Don't use DefaultNone derive; use #[derive(Default)] with #[default] attribute
• Method chaining in shaders: Use .method() not ::method() (e.g., Sdf2d.viewport(...))
• Color mixing: Prefer color1.mix(color2, hover) chaining over nested mix() calls
• Missing widget registration: Call crate::makepad_widgets::script_mod(vm) in App::run() BEFORE your own modules

Syntax Quick Reference

| Old (live_design!) | New (script_mod!) | |--------------------|-------------------| | <BaseWidget> | mod.widgets.BaseWidget{} or BaseWidget{} (if imported) | | {{StructName}} | #(Struct::register_widget(vm)) | | (THEME_COLOR_X) | theme.color_x | | <THEME_FONT> | theme.font_regular | | instance hover: 0.0 | hover: instance(0.0) | | uniform color: #fff | color: uniform(#fff) | | draw_bg: {} (replace) | draw_bg +: {} (merge) | | default: off | default: @off | | fn pixel(self) | pixel: fn() | | item.apply_over(cx, live!{...}) | script_apply_eval!(cx, item, {...}) |

Reference Files

• DSL Syntax Reference -- Complete syntax grammar and examples
• Property System -- Walk, Layout, Draw, and shader properties