deluge::hid::display::Starfield Class Reference

Perspective-projection starfield. More...

#include <starfield.h>

Classes
struct	Projected
	A star projected onto the screen. More...
struct	Star

Public Member Functions
	Starfield ()
	Construct a field that is already fully populated, so the first rendered frame is not empty.
void	scatter ()
	Re-scatter every star across the full depth range.
void	advance ()
	Advance every star one frame toward the viewer, respawning any that pass it.
Projected	project (size_t i) const
	Project a star onto the screen.
float	depthOf (size_t i) const
	Depth of a star. Exposed for tests.

Static Public Attributes
Field geometry
static constexpr size_t	kNumStars = 60
	Number of stars in the field.
static constexpr float	kMaxDepth = 32.0f
	Stars respawn at this depth once they pass the viewer.
static constexpr float	kZStep = 0.4f
	Depth consumed per frame.
static constexpr float	kFov = 3.14159265358979323846f
	Field of view, radians.
static constexpr float	kCentreX = 64.0f
	Projected screen centre, X, in pixels.
static constexpr float	kCentreY = 26.0f
	Projected screen centre, Y, in pixels: (OLED_MAIN_TOPMOST_PIXEL + OLED_MAIN_HEIGHT_PIXELS) / 2.
static constexpr float	kNearThreshold = kMaxDepth * 0.4f
static constexpr float	kMinDepth = 0.01f
	Floor applied to z when projecting.

Private Member Functions
uint32_t	nextRandom ()
	Step the linear congruential generator.
float	nextRandomFloat ()
	Step the linear congruential generator, mapped to [0, 1).
void	respawn (Star &star, float z)
	Give a star a fresh random x/y at the given depth.

Private Attributes
std::array< Star, kNumStars >	stars_ {}
uint32_t	rngState_ {0xCAFE5678}

Detailed Description

Perspective-projection starfield.

Stars hold a 3D position and are projected with factor = kFov / z, so they appear to fly toward the viewer as z decrements.

Note

Deliberately has no display dependency, so the projection maths is unit-testable on the host.

See also

The deluge-sdk demo firmware, firmwares/demo-firmware/src/tasks/oled.rs – the reference implementation this is ported from, and the source of the LCG constants and depth ranges.

Member Function Documentation

depthOf()

float deluge::hid::display::Starfield::depthOf ( size_t i ) const

inlinenodiscard

Depth of a star. Exposed for tests.

Parameters

i	Star index, less than kNumStars.

Returns

The star's z, always strictly positive.

nextRandom()

uint32_t deluge::hid::display::Starfield::nextRandom ( )

private

Step the linear congruential generator.

Returns

The next raw LCG output.

nextRandomFloat()

float deluge::hid::display::Starfield::nextRandomFloat ( )

private

Step the linear congruential generator, mapped to [0, 1).

Returns

The next LCG output, mapped to [0, 1).

project()

Starfield::Projected deluge::hid::display::Starfield::project ( size_t i ) const

nodiscard

Project a star onto the screen.

Parameters

i	Star index, less than kNumStars.

Returns

The star's unclipped screen position and pixel size.

respawn()

void deluge::hid::display::Starfield::respawn ( Star & star, float z )

private

Give a star a fresh random x/y at the given depth.

Parameters

star	The star to overwrite.
z	Depth to place it at.

scatter()

void deluge::hid::display::Starfield::scatter

(

)

Re-scatter every star across the full depth range.

Note

Does not reseed the LCG, so successive calls produce different fields.

Member Data Documentation

kMinDepth

float deluge::hid::display::Starfield::kMinDepth = 0.01f

staticconstexpr

Floor applied to z when projecting.

The reference implementation relies on Rust's saturating f32 as i32. A C++ static_cast of an out-of-range float is undefined behaviour, and z can land arbitrarily close to zero, so the projection factor is bounded instead.

Note

A star this close is off-screen and respawns next frame, so nothing visible changes.

kNearThreshold

float deluge::hid::display::Starfield::kNearThreshold = kMaxDepth * 0.4f

staticconstexpr

Depth threshold: stars nearer than this (same depth units as kMaxDepth) draw as 2x2 blocks rather than single pixels.

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The documentation for this class was generated from the following files:

• src/deluge/hid/display/starfield.h
• src/deluge/hid/display/starfield.cpp