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lightgrid_example.cpp
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lightgrid_example.cpp
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#include <string>
#include <iostream>
#include <vector>
#include <random>
#include <iomanip>
#include <SDL.h>
#include <lightgrid/grid.hpp>
#define WINDOW_WIDTH 1920
#define WINDOW_HEIGHT 1080
#define GRID_CELL_SIZE 10
#define NUM_ENTITIES 50000
#define LAYOUT_PADDING 1 // Number of pixels of separation between entities
#define MAX_ENTITY_WIDTH 5
#define MIN_ENTITY_WIDTH 5
#define MAX_ENTITY_HEIGHT (MAX_ENTITY_WIDTH)
#define MIN_ENTITY_HEIGHT (MIN_ENTITY_WIDTH)
// This collision simulation doesn't do anything fancy to deal with high-speed
// entities. For tiny entities, these speeds need to be fairly low to prevent
// entities from constantly flying through each other.
#define MAX_ENTITY_VELOCITY 15.0f
#define MIN_ENTITY_VELOCITY -15.0f
// SDL seems to use a massive amount of memory when drawing many rectangles.
// Still not sure if this is my issue, or SDL's issue; regardless, the memory
// usage is measured separately without the rectangles being rendered.
// I may convert to an OpenGL contect in the future.
// Setting this to true will disable SDL drawing
#define MEASURE_MEMORY false
SDL_Renderer *renderer;
SDL_Window *window;
SDL_Event event;
bool quit{false};
struct entity {
lightgrid::bounds bounds;
float velocity_x;
float velocity_y;
float real_x; // For pixel-width entities, the position must have
float real_y; // sub-pixel precision
SDL_Color color;
int grid_element_node; // When inserting an element into the grid, the
// Internal node in which the element was inserted is returned.
// This value must be known when removing an element from the
// grid.
// It was considered for the grid to keep track of this
// itself, but having the user of this library store a single
// integer along with the their own entity data seemed much more
// reasonable than requiring the user to provide a hash along
// with the type to be inserted, and then keeping a map to the
// element nodes interally. This may again be considered in the
// future though.
};
// While the grid's performance when querying will not suffer by holding the
// entities directly, there may be a performace penalty during insertion
// and retrieval as a copy of the type will be stored in the grid, and
// this will be copied.
// It is slightly prefered to insert pointers or indicies into other lists
// than it is to store an instance of that type.
lightgrid::grid<int, GRID_CELL_SIZE> grid;
std::vector<entity> entities;
// A vector (or some other insertable type) is needed to retrieve the values
// within the queried bounds.
// In a not-so-distant future version, a function such as iterQuery() will
// be implemented to avoid any costs associated with retrieval after
// a query in cases where the values returned are all passed to some
// functor.
std::vector<int> query;
std::mt19937 gen_rand;
lightgrid::bounds genBounds(int map_width, int map_height);
bool isColliding(const entity& e1, const entity& e2);
void resolveCollisionX(entity& e1, entity& e2);
void resolveCollisionY(entity& e1, entity& e2);
void resolveCollision(entity& e1, entity& e2);
void resolveCollisions();
void updatePositions(float delta_time);
void createEntities(int num_entities);
void prepareGrid();
void drawRects();
void pollEvents();
lightgrid::bounds genBounds(int map_width, int map_height) {
int w,h;
if (MAX_ENTITY_WIDTH != MIN_ENTITY_WIDTH) {
int rand_mod{MAX_ENTITY_WIDTH-MIN_ENTITY_WIDTH};
w = (int)(gen_rand()%(uint_fast32_t)(rand_mod)+MIN_ENTITY_WIDTH);
} else {
w = MAX_ENTITY_WIDTH;
}
if (MAX_ENTITY_HEIGHT != MIN_ENTITY_HEIGHT) {
int rand_mod{MAX_ENTITY_HEIGHT-MIN_ENTITY_HEIGHT};
h = (int)(gen_rand()%(uint_fast32_t)(rand_mod)+MIN_ENTITY_HEIGHT);
} else {
h = MAX_ENTITY_HEIGHT;
}
lightgrid::bounds new_bounds {
-1,-1,
w,h
};
return std::move(new_bounds);
}
// Simple aabb collision detection
bool isColliding(const entity& e1, const entity& e2) {
float top_1 = e1.real_y;
float bottom_1 = e1.real_y + e1.bounds.h;
float left_1 = e1.real_x;
float right_1 = e1.real_x + e1.bounds.w;
float top_2 = e2.real_y;
float bottom_2 = e2.real_y + e2.bounds.h;
float left_2 = e2.real_x;
float right_2 = e2.real_x + e2.bounds.w;
return (bottom_1 > top_2 && bottom_2 > top_1 && right_1 > left_2 && right_2 > left_1);
}
void resolveCollisionX(entity& e1, entity& e2) {
// All masses are assumed to be equal, so the resolution in either
// axis is as simple as setting the position of one entity
// to the edge of the other and swapping the velocities in that
// axis.
float tmp;
if (e1.real_x < e2.real_x) {
if (e1.velocity_x > e2.velocity_x) {
e1.real_x = e2.real_x - e1.bounds.w;
tmp = e1.velocity_x;
e1.velocity_x = e2.velocity_x;
e2.velocity_x = tmp;
}
} else {
if (e2.velocity_x > e1.velocity_x) {
e2.real_x = e1.real_x - e2.bounds.w;
tmp = e2.velocity_x;
e2.velocity_x = e1.velocity_x;
e1.velocity_x = tmp;
}
}
}
void resolveCollisionY(entity& e1, entity& e2) {
float tmp;
if (e1.real_y < e2.real_y) {
if (e1.velocity_y > e2.velocity_y) {
e1.real_y = e2.real_y - e1.bounds.h;
tmp = e1.velocity_y;
e1.velocity_y = e2.velocity_y;
e2.velocity_y = tmp;
}
} else {
if (e2.velocity_y > e1.velocity_y) {
e2.real_y = e1.real_y - e2.bounds.h;
tmp = e2.velocity_y;
e2.velocity_y = e1.velocity_y;
e1.velocity_y = tmp;
}
}
}
void resolveCollision(entity& e1, entity& e2) {
// For any collision between two aabb's, a collision only needs
// to be resolved in one axis.
// An intuitive solution for deciding which axis to resolve for
// is to imagine the rectangle create by the intersection
// of the two bounding boxes, and choose the axis perpendicular
// to the largest side of that intersection.
float collisions_width;
if (e1.real_x < e2.real_x) {
collisions_width = std::min((e1.real_x + e1.bounds.w) - e2.real_x, (float)e2.bounds.w);
} else {
collisions_width = std::min((e2.real_x + e2.bounds.w) - e1.real_x, (float)e1.bounds.w);
}
float collisions_height;
if (e1.real_y < e2.real_y) {
collisions_height = std::min((e1.real_y + e1.bounds.h) - e2.real_y, (float)e2.bounds.h);
} else {
collisions_height = std::min((e2.real_y + e2.bounds.h) - e1.real_y, (float)e1.bounds.h);
}
if (collisions_width > collisions_height) {
resolveCollisionY(e1, e2);
} else {
resolveCollisionX(e1,e2);
}
}
void resolveCollisions() {
for (int it{0}; it < entities.size(); it++) {
entity& entity{entities[it]};
// The list being used for querying exists outside of this scope and
// and is cleared as to avoid reallocation.
query.clear();
// The type of the results container must satisfy the lightgrid::insertable
// concept. After the query, the container will have had all the
// entities within the queried bounds inserted into it.
grid.query(entity.bounds, query);
// With the results in the "query" vector, it can be iterated over to find
// collisions among the other nearby entities.
for (auto& other_entity : query) {
if (it != other_entity && isColliding(entity, entities[other_entity])) {
resolveCollision(entity, entities[other_entity]);
}
}
if (entity.real_x <= 0) {
entity.real_x = 0;
entity.velocity_x = -entity.velocity_x;
}
if (entity.real_y <= 0) {
entity.real_y = 0;
entity.velocity_y = -entity.velocity_y;
}
if (entity.real_x + entity.bounds.w > WINDOW_WIDTH) {
entity.real_x = WINDOW_WIDTH - entity.bounds.w;
entity.velocity_x = -entity.velocity_x;
}
if (entity.real_y + entity.bounds.h > WINDOW_HEIGHT) {
entity.real_y = WINDOW_HEIGHT - entity.bounds.h;
entity.velocity_y = -entity.velocity_y;
}
}
}
void updatePositions(float delta_time) {
lightgrid::bounds old_bounds;
for (int it{0}; it < entities.size(); it++) {
entity& entity{entities[it]};
old_bounds = entity.bounds;
entity.real_x += (delta_time/1000.0)*entity.velocity_x;
entity.real_y += (delta_time/1000.0)*entity.velocity_y;
entity.bounds.x = entity.real_x;
entity.bounds.y = entity.real_y;
// The previous bounds are needed when updating the position of an
// element in the grid, along with the index of the element node,
// within the grid. This is the only overhead that must be
// considered when implementing the grid.
grid.update(entity.grid_element_node, old_bounds, entity.bounds);
}
}
void createEntities(int num_entities) {
// This function attempts to create the specified number of entities,
// centering them in the window. If specified number will not fit in
// the window, it will create as many entities as it can fit.
float ratio{WINDOW_WIDTH/(float)WINDOW_HEIGHT};
int padding{LAYOUT_PADDING};
int max_num_entities_y{WINDOW_HEIGHT/(MAX_ENTITY_HEIGHT+padding)};
int max_num_entities_x{WINDOW_WIDTH/(MAX_ENTITY_WIDTH+padding)};
int max_num_entities{max_num_entities_x*max_num_entities_y};
int width, start_x, start_y;
if (num_entities < max_num_entities) {
// Get the number of entities on a side
width = std::sqrt(ratio*num_entities);
int height{num_entities/width};
start_x = (max_num_entities_x - width)/2;
start_y = (max_num_entities_y - height)/2;
} else {
width = max_num_entities_x;
start_x = 0;
start_y = 0;
}
int entity_count{0};
uint8_t lowest_color{100};
for (int entity_count{0}; entity_count < num_entities && entity_count < max_num_entities; entity_count++) {
lightgrid::bounds new_bounds{genBounds(WINDOW_WIDTH, WINDOW_HEIGHT)};
float max_velocity{MAX_ENTITY_VELOCITY};
float min_velocity{MIN_ENTITY_VELOCITY};
float velocity_x{(gen_rand()%((uint_fast32_t)(max_velocity*100-min_velocity*100))/100.0f+min_velocity)};
float velocity_y{(gen_rand()%((uint_fast32_t)(max_velocity*100-min_velocity*100))/100.0f+min_velocity)};
int curr_x{(entity_count%width + start_x)*(MAX_ENTITY_WIDTH+padding)};
int curr_y{(entity_count/width + start_y)*(MAX_ENTITY_HEIGHT+padding)};
new_bounds.x = curr_x;
new_bounds.y = curr_y;
entities.emplace_back(
new_bounds,
velocity_x,
velocity_y, // velocity
curr_x,
curr_y,
(SDL_Color) {
(uint8_t)(lowest_color + (gen_rand()%(256 - lowest_color))),
(uint8_t)(lowest_color + (gen_rand()%(256 - lowest_color))),
(uint8_t)(lowest_color + (gen_rand()%(256 - lowest_color))),
255
}
);
}
}
void prepareGrid() {
// grid.init(WINDOW_WIDTH, WINDOW_HEIGHT, GRID_CELL_SIZE);
grid.reserve(entities.size());
query.reserve(entities.size());
for (int it{0}; it < entities.size(); it++) {
// When inserting into the grid, the index of the internal element node must be stored somewhere.
entities[it].grid_element_node= grid.insert(it, entities[it].bounds);
}
}
void drawRects() {
for (auto entity : entities) {
SDL_SetRenderDrawColor(renderer, entity.color.r, entity.color.g, entity.color.b, 255);
SDL_RenderFillRect(renderer, reinterpret_cast<SDL_Rect*>(&(entity.bounds)));
}
}
void pollEvents() {
while (SDL_PollEvent(&event) == 1) {
switch(event.type) {
case SDL_QUIT:
quit = true;
break;
case SDL_KEYDOWN:
switch(event.key.keysym.sym) {
case SDLK_ESCAPE:
quit = true;
break;
}
break;
}
}
}
int main(int argc, char **argv) {
SDL_Init(SDL_INIT_TIMER | SDL_INIT_VIDEO);
SDL_CreateWindowAndRenderer(WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &renderer);
createEntities(NUM_ENTITIES);
prepareGrid();
std::cout << "Number of entities: " << entities.size() << "\n";
uint64_t last_frame{SDL_GetTicks64()};
uint64_t current_frame{SDL_GetTicks64()};
uint64_t delta_time{0};
int frame_count{0};
uint64_t interval_time{0};
while (!quit) {
pollEvents();
current_frame = SDL_GetTicks64();
delta_time = current_frame - last_frame;
last_frame = current_frame;
SDL_SetRenderDrawColor(renderer, 40, 35, 30, 0);
SDL_RenderClear(renderer);
updatePositions(delta_time);
resolveCollisions();
#if !(MEASURE_MEMORY)
drawRects();
#endif
SDL_RenderPresent(renderer);
frame_count++;
interval_time += delta_time;
if (interval_time >= 1000) {
std::cout << "\r" << std::fixed << std::setprecision(2) << "FPS: " << std::setw(10) << (frame_count/(float)interval_time)*1000.0f;
frame_count = 0;
interval_time = 0;
}
}
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}