PIGO8 Transparency Management

PIGO8 uses binary transparency, where each color in the palette is either fully visible or fully transparent. By default, only color 0 (black) is transparent. You can change which colors are transparent to create various visual effects.

Function

Palt

func Palt(args ...interface{})

PICO-8 style function for setting color transparency. This function has multiple usage patterns:

  1. Palt() - Reset all transparency settings to default (only color 0 is transparent)
  2. Palt(colorIndex, transparent) - Set a specific color's transparency

Parameters:

  • colorIndex: Index of the color in the palette.
  • transparent: Whether the color should be transparent (true) or opaque (false).

Example:

// Make color 0 opaque and color 1 transparent
pigo8.Palt(0, false)
pigo8.Palt(1, true)

// Reset to default (only color 0 is transparent)
pigo8.Palt()

How Transparency Works

When drawing sprites, pixels with transparent colors are not drawn, allowing the background to show through. This is useful for:

  1. Creating sprites with irregular shapes
  2. Layering sprites on top of each other
  3. Creating special effects

The transparency is checked in drawing functions like Spr(), Sspr(), and Pset().

Advanced Usage Examples

Creating a Sprite Mask

// Draw a background
pigo8.Rectfill(0, 0, 127, 127, 12) // Fill screen with blue

// Set red (color 8) as transparent
pigo8.Palt(8, true)

// Draw a sprite where all red pixels will be transparent
pigo8.Spr(0, 64, 64, 1, 1)

// Reset transparency to default
pigo8.Palt()

Multiple Transparent Colors

// Make both black (0) and white (7) transparent
pigo8.Palt(0, true)
pigo8.Palt(7, true)

// Draw sprite with both black and white areas transparent
pigo8.Spr(1, 10, 10, 1, 1)

// Reset to default
pigo8.Palt()

Swapping Transparent Colors

// Make black (0) opaque and blue (12) transparent
pigo8.Palt(0, false)
pigo8.Palt(12, true)

// Draw sprites with this new transparency setting
pigo8.Spr(2, 20, 20, 1, 1)

// Reset to default
pigo8.Palt()

Creating a Cutout Effect

// Draw a colorful background
for y := 0; y < 128; y += 8 {
    for x := 0; x < 128; x += 8 {
        pigo8.Rectfill(x, y, x+7, y+7, (x+y) % pigo8.GetPaletteSize())
    }
}

// Make white (7) transparent
pigo8.Palt(7, true)

// Draw a sprite with white areas that act as "windows" to the background
pigo8.Spr(3, 32, 32, 2, 2)

Best Practices

  1. Reset transparency when you're done with special effects to avoid unexpected behavior.
  2. Be consistent with your transparency usage to avoid confusion.
  3. Document your transparency choices in your code with comments.
  4. Consider performance - using many transparent colors can make your code harder to understand.
  5. Test thoroughly - transparency effects can sometimes be subtle and may not work as expected on all backgrounds.

Transparency and Custom Palettes

When you use SetPalette() to change the palette, the transparency array is automatically resized to match. The function preserves existing transparency settings for colors that still exist in the new palette and ensures that color 0 is transparent by default.

// Create a custom palette
customPalette := []color.Color{
    color.RGBA{0, 0, 0, 255},     // Black
    color.RGBA{255, 0, 0, 255},   // Red
    color.RGBA{0, 255, 0, 255},   // Green
    color.RGBA{0, 0, 255, 255},   // Blue
}

// Set the palette - color 0 will be transparent by default
pigo8.SetPalette(customPalette)

// Make red (color 1) transparent as well
pigo8.Palt(1, true)