Struct Color555

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pub struct Color555(/* private fields */);

Expand description

A 15-bit BGR pixel as stored in VRAM.

PSX VRAM stores every halfword in BGR-555-with-mask-bit layout:

  bit  15   14..10   9..5   4..0
       m    B       G      R

The mask bit is bit 15; Color555::rgb8 constructs with the mask bit clear (most common). The “transparency” that games rely on for CLUT sprites is Color555::raw(0) – PSX treats an all-zero texel as transparent in direct-color mode.

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impl Color555

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pub const TRANSPARENT: Self

Fully-transparent texel (value 0). PSX treats this as “skip” when sampling a textured primitive, regardless of mode.

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pub const BLACK: Self

Opaque black with mask bit clear.

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pub const WHITE: Self

Opaque white – all five bits set in each channel.

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pub const fn rgb8(r: u8, g: u8, b: u8) -> Self

Build a color from 8-bit channels, truncating the low 3 bits of each. rgb8(255, 255, 255) == WHITE.

Matches PsyQ’s getTPage(0, r, g, b) and setRGB0(prim, r, g, b) convention where the caller writes 8-bit values; hardware sees 5 bits per channel.

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pub const fn rgb5(r: u8, g: u8, b: u8) -> Self

Build a color from already-5-bit channels. Asserts each fits in 5 bits. rgb5(31, 31, 31) == WHITE.

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pub const fn raw(value: u16) -> Self

Construct from the raw VRAM halfword. Useful when decoding CLUT bytes or loading pre-packed asset data.

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pub const fn as_u16(self) -> u16

Underlying VRAM halfword.

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pub const fn with_mask_bit(self) -> Self

Set the mask bit (bit 15). Matters when GP0 0xE6 has “check mask on draw” enabled – writes are skipped where existing mask is set. Games use this for UI overlays.

In a CLUT entry bit 15 means something else entirely: see Self::with_semi_transparency.

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pub const fn with_semi_transparency(self) -> Self

Set the semi-transparency bit (STP, bit 15) for use in a CLUT entry.

This is the same bit as Self::with_mask_bit, but when the halfword is a palette entry rather than a framebuffer pixel the GPU reads it as “blend this texel”. Selecting a blend mode on a textured primitive is not enough on its own: the mode says how to blend, STP says which texels blend. A palette without it draws fully opaque whatever blend mode the primitive carries, and nothing reports it – a silent failure that reads like a brightness bug rather than a blending one.

Set it on every entry of an additive or translucent palette, leaving the fully transparent index (usually 0) at Self::TRANSPARENT.

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