billboard_sorter.c File Reference

Back-to-front sorting for transparent billboard geometry. More...

#include "billboard_sorter.h"
#include "gl_common.h"
#include "gl_debug.h"
#include "log.h"
#include "platform/platform_utils.h"
#include "profiler.h"
#include "scene_config.h"
#include "shader.h"
#include "sphere_types.h"
#include <cglm/types.h>
#include <cglm/vec3.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>

Include dependency graph for billboard_sorter.c:

Enumerations
enum	{ EXPECTED_SPHERE_INSTANCE_SIZE = 128 }
enum	{   WORKGROUP_SIZE = 1024 , DEFAULT_MIN_CAPACITY = 64 , MAX_SINGLE_PASS_COUNT = 1024 , RADIX_BITS_PER_PASS = 8 ,   RADIX_BUCKETS = 256 , RADIX_SHIFT_LIMIT = 32 , RADIX_MASK = 0xFF }

Functions
static int	next_pow2 (int val)
static bool	ensure_cpu_capacity (BillboardSorter *sorter, int count)
	Grow CPU scratchpads to hold at least count elements.
static GLuint	upload_sorted_to_ssbo (BillboardSorter *sorter, int count)
	Upload count sorted instances from the CPU temp buffer to the SSBO.
void	billboard_sorter_init (BillboardSorter *sorter, int initial_capacity)
	Allocates internal buffers for the sorter.
void	billboard_sorter_cleanup (BillboardSorter *sorter)
	Destroys the sorter context.
GLuint	billboard_sorter_sort_gpu (BillboardSorter *sorter, const SphereInstance *instances, int count, const vec3 camera_pos)
	Sorts the array of instances Back-to-Front (descending depth) on GPU.
static int	compare_sphere_entries (const void *lhs, const void *rhs)
GLuint	billboard_sorter_sort_cpu (BillboardSorter *sorter, const SphereInstance *instances, int count, const vec3 camera_pos)
	Sorts the array of instances Back-to-Front (descending depth) on CPU.
static uint32_t	float_to_sortable_uint (float f_val)
	Converts a float to a uint32_t that preserves order (IEEE 754). This allows sorting floats using integer radix sort.
GLuint	billboard_sorter_sort_cpu_radix (BillboardSorter *sorter, const SphereInstance *instances, int count, const vec3 camera_pos)
	Sorts the array of instances Back-to-Front (descending depth) using Radix Sort.
GLuint	billboard_sorter_sort (BillboardSorter *sorter, const SphereInstance *instances, int count, const vec3 camera_pos, SortingMode mode)
	Dispatches the sorting task using the specified SortingMode.

Variables
static const uint32_t	FLOAT_SIGN_MASK = 0x80000000U
static const uint32_t	FLOAT_COMPLEMENT_MASK = 0xFFFFFFFFU
static const unsigned int	BIT_SHIFT_8 = 8U
static const unsigned int	BIT_SHIFT_16 = 16U
static const size_t	GPU_ENTRY_SIZE = 8

Detailed Description

Back-to-front sorting for transparent billboard geometry.

Enumeration Type Documentation

anonymous enum

anonymous enum

Enumerator
EXPECTED_SPHERE_INSTANCE_SIZE

anonymous enum

anonymous enum

Enumerator
WORKGROUP_SIZE
DEFAULT_MIN_CAPACITY
MAX_SINGLE_PASS_COUNT
RADIX_BITS_PER_PASS
RADIX_BUCKETS
RADIX_SHIFT_LIMIT
RADIX_MASK

Function Documentation

billboard_sorter_cleanup()

void billboard_sorter_cleanup

(

BillboardSorter *

sorter

)

Destroys the sorter context.

Parameters

sorter

Pointer to the struct.

billboard_sorter_init()

void billboard_sorter_init	(	BillboardSorter *	sorter,
		int	initial_capacity
	)

Allocates internal buffers for the sorter.

Parameters

sorter	Pointer to the struct.
initial_capacity	Expected number of instances.

Here is the call graph for this function:

billboard_sorter_sort()

GLuint billboard_sorter_sort	(	BillboardSorter *	sorter,
		const SphereInstance *	instances,
		int	count,
		const vec3	camera_pos,
		SortingMode	mode
	)

Dispatches the sorting task using the specified SortingMode.

Parameters

sorter	Memory context.
instances	Array of instances.
count	Active element count.
camera_pos	World-space viewer position.
mode	Sorting algorithm choice.

Returns

The SSBO handle containing the sorted instances.

Here is the call graph for this function:

billboard_sorter_sort_cpu()

GLuint billboard_sorter_sort_cpu	(	BillboardSorter *	sorter,
		const SphereInstance *	instances,
		int	count,
		const vec3	camera_pos
	)

Sorts the array of instances Back-to-Front (descending depth) on CPU.

Parameters

sorter	Memory context.
instances	Array of instances (will be copied and sorted internally).
count	Active element count.
camera_pos	World-space viewer position.

Returns

The SSBO handle containing the sorted instances.

Here is the call graph for this function:

billboard_sorter_sort_cpu_radix()

GLuint billboard_sorter_sort_cpu_radix	(	BillboardSorter *	sorter,
		const SphereInstance *	instances,
		int	count,
		const vec3	camera_pos
	)

Sorts the array of instances Back-to-Front (descending depth) using Radix Sort.

Parameters

sorter	Memory context.
instances	Array of instances.
count	Active element count.
camera_pos	World-space viewer position (for depth).

Returns

The SSBO handle containing the sorted instances.

Here is the call graph for this function:

billboard_sorter_sort_gpu()

GLuint billboard_sorter_sort_gpu	(	BillboardSorter *	sorter,
		const SphereInstance *	instances,
		int	count,
		const vec3	camera_pos
	)

Sorts the array of instances Back-to-Front (descending depth) on GPU.

Parameters

sorter	Memory context.
instances	Pointer to the array of instances to upload.
count	Active element count.
camera_pos	World-space viewer position.

Returns

The SSBO handle containing the sorted instances.

Here is the call graph for this function:

compare_sphere_entries()

static int compare_sphere_entries ( const void *  lhs, const void *  rhs  )

static

ensure_cpu_capacity()

static bool ensure_cpu_capacity ( BillboardSorter *  sorter, int  count  )

static

Grow CPU scratchpads to hold at least count elements.

Returns

true on success, false on allocation failure.

float_to_sortable_uint()

static uint32_t float_to_sortable_uint ( float  f_val )

inlinestatic

Converts a float to a uint32_t that preserves order (IEEE 754). This allows sorting floats using integer radix sort.

next_pow2()

static int next_pow2 ( int  val )

static

upload_sorted_to_ssbo()

static GLuint upload_sorted_to_ssbo ( BillboardSorter *  sorter, int  count  )

static

Upload count sorted instances from the CPU temp buffer to the SSBO.

Returns

The SSBO handle containing the data.

Variable Documentation

BIT_SHIFT_16

const unsigned int BIT_SHIFT_16 = 16U

static

BIT_SHIFT_8

const unsigned int BIT_SHIFT_8 = 8U

static

Bit-shift constants for next_pow2 (named to satisfy linter).

FLOAT_COMPLEMENT_MASK

const uint32_t FLOAT_COMPLEMENT_MASK = 0xFFFFFFFFU

static

FLOAT_SIGN_MASK

const uint32_t FLOAT_SIGN_MASK = 0x80000000U

static

GPU_ENTRY_SIZE

const size_t GPU_ENTRY_SIZE = 8

static

Size of the Entry struct in the compute shader: int (4) + float (4).