trail_renderer.h File Reference

GPU-accelerated ribbon trail renderer for N-body simulation. More...

#include "gl_common.h"
#include "nbody.h"
#include <cglm/types.h>
#include <stdbool.h>

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Data Structures
struct	TrailVertex
	Per-vertex data for the ribbon triangle strip. More...
struct	TrailRing
	Ring buffer of recorded positions for one body. More...
struct	TrailNeonParams
	Runtime-adjustable neon glow profile parameters. More...
struct	TrailRenderer
	Manages trail state and GPU resources for all bodies. More...

Enumerations
enum	{ TRAIL_MAX_POINTS = 256 }
enum	TrailNeonParam { TRAIL_NEON_PARAM_INTENSITY = 0 , TRAIL_NEON_PARAM_CORE , TRAIL_NEON_PARAM_WIDTH , TRAIL_NEON_PARAM_COUNT }
	Identifies which neon parameter is being adjusted. More...

Functions
bool	trail_renderer_init (TrailRenderer *tr, int body_count)
	Initializes trail renderer resources.
void	trail_renderer_set_color (TrailRenderer *tr, int body_index, const vec3 color)
	Sets the trail color for a specific body.
void	trail_renderer_record (TrailRenderer *tr, const NBodySim *sim, float delta_time)
	Records current positions from the simulation.
float	trail_renderer_get_duration (const TrailRenderer *tr)
	Returns the current trail duration in seconds.
void	trail_renderer_set_duration (TrailRenderer *tr, float duration)
	Sets the trail duration in seconds (clamped to valid range).
void	trail_renderer_draw (TrailRenderer *tr, mat4 view, mat4 proj, vec3 cam_pos)
	Builds ribbon geometry and renders all trails.
void	trail_renderer_clear (TrailRenderer *tr)
	Clears all recorded trail data (e.g., on simulation reset).
void	trail_renderer_cleanup (TrailRenderer *tr)
	Releases all GPU resources.

Variables
static const float	TRAIL_HDR_INTENSITY = 5.0F
static const float	TRAIL_MAX_WIDTH = 0.24F
static const float	TRAIL_SAMPLE_INTERVAL = 1.0F / 60.0F
static const float	TRAIL_DURATION_DEFAULT = 4.0F
static const float	TRAIL_DURATION_MIN = 0.5F
static const float	TRAIL_DURATION_MAX = 30.0F
static const float	TRAIL_DURATION_STEP = 0.5F
static const float	TRAIL_NEON_INTENSITY_DEFAULT = 5.0F
static const float	TRAIL_NEON_CORE_EXP_DEFAULT = 12.0F
static const float	TRAIL_NEON_WIDTH_DEFAULT = 0.24F
static const float	TRAIL_NEON_INTENSITY_STEP = 0.5F
static const float	TRAIL_NEON_CORE_STEP = 2.0F
static const float	TRAIL_NEON_WIDTH_STEP = 0.02F
static const float	TRAIL_NEON_INTENSITY_MIN = 0.5F
static const float	TRAIL_NEON_CORE_MIN = 2.0F
static const float	TRAIL_NEON_WIDTH_MIN = 0.04F

Detailed Description

GPU-accelerated ribbon trail renderer for N-body simulation.

Records positions over time for each body and renders camera-facing ribbon geometry with:

• Width tapering (thick at head, zero at tail)
• Soft anti-aliased edges via fragment shader smoothstep
• HDR emissive colors for bloom integration
• Additive blending for glow accumulation

Enumeration Type Documentation

anonymous enum

anonymous enum

Maximum trail sample points per body.

Enumerator
TRAIL_MAX_POINTS

TrailNeonParam

enum TrailNeonParam

Identifies which neon parameter is being adjusted.

Enumerator
TRAIL_NEON_PARAM_INTENSITY
TRAIL_NEON_PARAM_CORE
TRAIL_NEON_PARAM_WIDTH
TRAIL_NEON_PARAM_COUNT

Function Documentation

trail_renderer_cleanup()

void trail_renderer_cleanup

(

TrailRenderer *

tr

)

Releases all GPU resources.

Parameters

tr	Pointer to the trail renderer.

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trail_renderer_clear()

void trail_renderer_clear

(

TrailRenderer *

tr

)

Clears all recorded trail data (e.g., on simulation reset).

Parameters

tr	Pointer to the trail renderer.

trail_renderer_draw()

void trail_renderer_draw	(	TrailRenderer *	tr,
		mat4	view,
		mat4	proj,
		vec3	cam_pos
	)

Builds ribbon geometry and renders all trails.

Must be called while the HDR framebuffer is active (before post-process). Sets up additive blending and depth-read-no-write internally.

Parameters

tr	Pointer to the trail renderer.
view	View matrix.
proj	Projection matrix.
cam_pos	Camera world position.

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trail_renderer_get_duration()

float trail_renderer_get_duration

(

const TrailRenderer *

tr

)

Returns the current trail duration in seconds.

trail_renderer_init()

bool trail_renderer_init	(	TrailRenderer *	tr,
		int	body_count
	)

Initializes trail renderer resources.

Parameters

tr	Pointer to the trail renderer.
body_count	Number of bodies to track.

Returns

true on success, false on failure.

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trail_renderer_record()

void trail_renderer_record	(	TrailRenderer *	tr,
		const NBodySim *	sim,
		float	delta_time
	)

Records current positions from the simulation.

Should be called every frame. Internally rate-limits sampling.

Parameters

tr	Pointer to the trail renderer.
sim	Pointer to the N-body simulation.
delta_time	Frame delta time.

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trail_renderer_set_color()

void trail_renderer_set_color	(	TrailRenderer *	tr,
		int	body_index,
		const vec3	color
	)

Sets the trail color for a specific body.

Parameters

tr	Pointer to the trail renderer.
body_index	Body index.
color	HDR emissive color (values > 1.0 are valid for bloom).

trail_renderer_set_duration()

void trail_renderer_set_duration	(	TrailRenderer *	tr,
		float	duration
	)

Sets the trail duration in seconds (clamped to valid range).

Variable Documentation

TRAIL_DURATION_DEFAULT

const float TRAIL_DURATION_DEFAULT = 4.0F

static

Default trail duration in seconds (how long a trail persists).

TRAIL_DURATION_MAX

const float TRAIL_DURATION_MAX = 30.0F

static

TRAIL_DURATION_MIN

const float TRAIL_DURATION_MIN = 0.5F

static

Minimum / maximum trail duration for runtime adjustment.

TRAIL_DURATION_STEP

const float TRAIL_DURATION_STEP = 0.5F

static

TRAIL_HDR_INTENSITY

const float TRAIL_HDR_INTENSITY = 5.0F

static

HDR intensity multiplier — drives bloom for neon glow effect.

TRAIL_MAX_WIDTH

const float TRAIL_MAX_WIDTH = 0.24F

static

Maximum ribbon half-width in world units.

TRAIL_NEON_CORE_EXP_DEFAULT

const float TRAIL_NEON_CORE_EXP_DEFAULT = 12.0F

static

TRAIL_NEON_CORE_MIN

const float TRAIL_NEON_CORE_MIN = 2.0F

static

TRAIL_NEON_CORE_STEP

const float TRAIL_NEON_CORE_STEP = 2.0F

static

TRAIL_NEON_INTENSITY_DEFAULT

const float TRAIL_NEON_INTENSITY_DEFAULT = 5.0F

static

Default neon parameter values.

TRAIL_NEON_INTENSITY_MIN

const float TRAIL_NEON_INTENSITY_MIN = 0.5F

static

TRAIL_NEON_INTENSITY_STEP

const float TRAIL_NEON_INTENSITY_STEP = 0.5F

static

TRAIL_NEON_WIDTH_DEFAULT

const float TRAIL_NEON_WIDTH_DEFAULT = 0.24F

static

TRAIL_NEON_WIDTH_MIN

const float TRAIL_NEON_WIDTH_MIN = 0.04F

static

TRAIL_NEON_WIDTH_STEP

const float TRAIL_NEON_WIDTH_STEP = 0.02F

static

TRAIL_SAMPLE_INTERVAL

const float TRAIL_SAMPLE_INTERVAL = 1.0F / 60.0F

static

Minimum time between trail samples (seconds).