FlexLove/themes/README.md

FlexLove Theme System

Overview

FlexLove supports a flexible 9-slice/9-patch theming system that allows you to create scalable UI components using texture atlases. Themes provide state-based visual feedback and automatically handle element sizing.

Key Features

• 9-Slice Scaling: Images scale properly to any size without distortion
• State Management: Automatic visual feedback for hover, pressed, disabled, and active states
• Layered Rendering: Themes render on top of backgroundColor, with borders on top
• Flexible Organization: Use separate images, single atlas, or hybrid approach
• Automatic Highlight Disable: Elements with themes automatically disable the pressed overlay

Image Organization Options

You have three ways to organize your theme images:

Option 1: Separate Images Per Component (Recommended for Beginners)

Each component gets its own image file:

themes/
  panel.png           (24x24 pixels - 9-slice for panels)
  button_normal.png   (24x24 pixels - 9-slice for buttons)
  button_hover.png    (24x24 pixels - hover state)
  button_pressed.png  (24x24 pixels - pressed state)
  input.png           (24x24 pixels - 9-slice for inputs)

Theme definition:

return {
  name = "My Theme",
  components = {
    panel = {
      atlas = "themes/panel.png",
      regions = { ... }
    },
    button = {
      atlas = "themes/button_normal.png",
      regions = { ... },
      states = {
        hover = {
          atlas = "themes/button_hover.png",
          regions = { ... }
        },
        pressed = {
          atlas = "themes/button_pressed.png",
          regions = { ... }
        }
      }
    }
  }
}

Option 2: Single Atlas (Recommended for Performance)

All components in one texture atlas:

themes/
  default_atlas.png   (96x48 pixels containing all components)

Theme definition:

return {
  name = "My Theme",
  atlas = "themes/default_atlas.png",  -- Global atlas
  components = {
    panel = {
      regions = {
        topLeft = {x=0, y=0, w=8, h=8},
        -- ... regions reference positions in atlas
      }
    },
    button = {
      regions = {
        topLeft = {x=24, y=0, w=8, h=8},  -- Different position in same atlas
        -- ...
      }
    }
  }
}

Option 3: Hybrid (Best of Both Worlds)

Mix global atlas with component-specific images:

return {
  name = "My Theme",
  atlas = "themes/global_atlas.png",  -- Fallback atlas
  components = {
    panel = {
      -- Uses global atlas
      regions = {x=0, y=0, ...}
    },
    button = {
      atlas = "themes/button.png",  -- Override with specific image
      regions = {x=0, y=0, ...}
    }
  }
}

9-Slice Structure

Each component image is divided into 9 regions:

┌─────┬──────────┬─────┐
│ TL  │   TC     │ TR  │  (Top: fixed height)
├─────┼──────────┼─────┤
│ ML  │   MC     │ MR  │  (Middle: stretches)
├─────┼──────────┼─────┤
│ BL  │   BC     │ BR  │  (Bottom: fixed height)
└─────┴──────────┴─────┘
 Fixed  Stretch  Fixed

• Corners (TL, TR, BL, BR): Fixed size, never stretched
• Edges (TC, BC, ML, MR): Stretched in one direction
• Center (MC): Stretched in both directions

Creating Theme Images

Minimum Image Size

For a 9-slice image, you need at least 24x24 pixels:

• 8px for each corner
• 8px for stretchable middle section

Image Requirements

1. Format: PNG with transparency
2. Color Mode: RGBA
3. Border Style: Draw borders in the corner/edge regions
4. Center: Can be solid color or transparent

Example: Creating a Button Image

For a button with rounded corners and a border:

button_normal.png (24x24 pixels)

Pixel layout:
┌────────┬────────────┬────────┐
│ ●●●●●● │ ██████████ │ ●●●●●● │  8px
│ ●●●●●● │ ██████████ │ ●●●●●● │
├────────┼────────────┼────────┤
│ ██████ │ ░░░░░░░░░░ │ ██████ │  8px (stretch)
│ ██████ │ ░░░░░░░░░░ │ ██████ │
├────────┼────────────┼────────┤
│ ●●●●●● │ ██████████ │ ●●●●●● │  8px
│ ●●●●●● │ ██████████ │ ●●●●●● │
└────────┴────────────┴────────┘
  8px     8px(stretch)   8px

Legend:
● = Corner (fixed)
█ = Border edge (stretched)
░ = Fill/background (stretched both ways)

Usage in Code

local FlexLove = require("FlexLove")
local Theme = FlexLove.Theme
local Gui = FlexLove.Gui
local Color = FlexLove.Color

-- Load theme
Theme.load("my_theme")
Theme.setActive("my_theme")

-- Create themed button
local button = Gui.new({
  width = 150,
  height = 40,
  text = "Click Me",
  textAlign = "center",
  textColor = Color.new(1, 1, 1, 1),
  backgroundColor = Color.new(0.2, 0.4, 0.8, 0.3),  -- Shows behind theme
  themeComponent = "button",  -- Uses button component from active theme
  callback = function(element, event)
    if event.type == "click" then
      print("Clicked!")
    end
  end
})

-- Create themed panel
local panel = Gui.new({
  width = 300,
  height = 200,
  backgroundColor = Color.new(0.1, 0.1, 0.2, 0.5),  -- Background tint
  themeComponent = "panel"
})

Rendering Layers

Elements with themes render in this order:

1. backgroundColor - Rendered first (behind everything)
2. Theme 9-slice - Rendered on top of backgroundColor
3. Borders - Rendered on top of theme (if specified)
4. Text - Rendered last (on top of everything)

This allows you to:

• Tint themed elements with backgroundColor
• Add custom borders on top of themes
• Layer visual effects

Component States

Themes automatically handle visual states for interactive elements:

• normal: Default appearance
• hover: When mouse is over the element
• pressed: When element is being clicked
• disabled: When element.disabled = true
• active: When element.active = true (for inputs/focused elements)

Define state-specific images in your theme:

button = {
  atlas = "themes/button_normal.png",
  regions = { ... },
  states = {
    hover = {
      atlas = "themes/button_hover.png",
      regions = { ... }
    },
    pressed = {
      atlas = "themes/button_pressed.png",
      regions = { ... }
    },
    disabled = {
      atlas = "themes/button_disabled.png",
      regions = { ... }
    }
  }
}

Theme Definition Example

-- themes/my_theme.lua
return {
  name = "My Theme",
  atlas = "themes/my_theme/atlas.png",
  
  components = {
    panel = {
      regions = {
        topLeft = {x=0, y=0, w=8, h=8},
        topCenter = {x=8, y=0, w=8, h=8},
        topRight = {x=16, y=0, w=8, h=8},
        middleLeft = {x=0, y=8, w=8, h=8},
        middleCenter = {x=8, y=8, w=8, h=8},
        middleRight = {x=16, y=8, w=8, h=8},
        bottomLeft = {x=0, y=16, w=8, h=8},
        bottomCenter = {x=8, y=16, w=8, h=8},
        bottomRight = {x=16, y=16, w=8, h=8}
      }
    },
    
    button = {
      regions = {
        topLeft = {x=24, y=0, w=8, h=8},
        topCenter = {x=32, y=0, w=8, h=8},
        topRight = {x=40, y=0, w=8, h=8},
        middleLeft = {x=24, y=8, w=8, h=8},
        middleCenter = {x=32, y=8, w=8, h=8},
        middleRight = {x=40, y=8, w=8, h=8},
        bottomLeft = {x=24, y=16, w=8, h=8},
        bottomCenter = {x=32, y=16, w=8, h=8},
        bottomRight = {x=40, y=16, w=8, h=8}
      },
      states = {
        hover = {
          regions = {
            -- Different region coordinates for hover state
            topLeft = {x=48, y=0, w=8, h=8},
            -- ... etc
          }
        },
        pressed = {
          regions = {
            -- Different region coordinates for pressed state
            topLeft = {x=72, y=0, w=8, h=8},
            -- ... etc
          }
        }
      }
    }
  }
}

Advanced Features

Automatic Highlight Disable

Elements with themeComponent automatically set disableHighlight = true to prevent the default gray pressed overlay from interfering with theme visuals. You can override this:

Gui.new({
  themeComponent = "button",
  disableHighlight = false,  -- Force enable highlight overlay
  -- ...
})

Combining with Corner Radius

You can use cornerRadius with themed elements:

Gui.new({
  themeComponent = "button",
  cornerRadius = 10,  -- Clips theme to rounded corners
  -- ...
})

Border Overlay

Add custom borders on top of themes:

Gui.new({
  themeComponent = "panel",
  border = { top = true, bottom = true, left = true, right = true },
  borderColor = Color.new(1, 1, 0, 1),  -- Yellow border on top of theme
  -- ...
})

Corner Scaling

By default, 9-slice corners and non-stretched edges are rendered at their original pixel size (1:1). You can scale corners using a numeric multiplier:

Corner Scaling

-- themes/my_theme.lua
return {
  name = "My Theme",
  components = {
    button = {
      atlas = "themes/button.png",
      insets = { left = 8, top = 8, right = 8, bottom = 8 },
      scaleCorners = 2,                 -- Scale corners by 2x (numeric multiplier)
      scalingAlgorithm = "bilinear"     -- "bilinear" (smooth) or "nearest" (sharp/pixelated)
    }
  }
}

scaleCorners values:

• Number (e.g., 2, 1.5, 0.5) - Direct scale multiplier
  • 2 = double size
  • 0.5 = half size
  • 1 = original size
• nil (default) - No scaling, 1:1 pixel perfect

Scaling Algorithms

• bilinear (default): Smooth interpolation between pixels. Best for most use cases.
• nearest: Nearest-neighbor sampling. Best for pixel art that should maintain sharp edges.

When to Use Corner Scaling

• Pixel art themes: Use scaleCorners = 2 with scalingAlgorithm = "nearest" to maintain crisp pixel boundaries
• High DPI displays: Use scaleCorners = 1.5 or 2 with scalingAlgorithm = "bilinear" for smooth scaling
• Fixed-size UI: Keep scaleCorners = nil (default) for pixel-perfect rendering at original size

Per-State Scaling

You can also set scaling per-state:

button = {
  atlas = "themes/button_normal.png",
  scaleCorners = 2,
  scalingAlgorithm = "bilinear",
  states = {
    hover = {
      atlas = "themes/button_hover.png",
      scaleCorners = 2.5,              -- Can override per state
      scalingAlgorithm = "nearest"     -- Different algorithm for this state
    }
  }
}

Tips

1. Start Simple: Begin with one component (button) before creating a full theme
2. Test Scaling: Make sure your 9-slice regions stretch properly at different sizes
3. Consistent Style: Keep corner sizes consistent across components
4. State Variations: For button states, change colors/brightness rather than structure
5. Atlas Packing: Use tools like TexturePacker or Aseprite to create efficient atlases
6. Transparency: Use semi-transparent backgroundColor to tint themed elements
7. Corner Scaling: Enable for pixel art or responsive UIs; disable for pixel-perfect rendering

Tools for Creating Atlases

• TexturePacker: Professional sprite sheet tool
• Aseprite: Pixel art editor with export options
• Shoebox: Free sprite sheet packer
• GIMP/Photoshop: Manual layout with guides

Example Themes

See the space/ directory for a complete theme example with:

• Panel component
• Button component with states (normal, hover, pressed, disabled)
• Compressed and uncompressed versions

See Also

• space.lua - Complete theme definition example
• ThemeSystemDemo.lua - Interactive demo of theme system
• ThemeLayeringDemo.lua - Demo of backgroundColor/theme/border layering