[游戏开发]OpenGL-实战篇--Breakout--Particles--51

学习链接：中文---------英语原文

这一节主要讲粒子，还是不较好理解的，类似Unity的粒子系统，但这里是比较简单的。

ParticleGenerator.h:

#pragma once

//注意把Shader.h放在前面
#include "Shader.h"
#include <GLFW/glfw3.h>
#include <glm/glm.hpp>
#include "Texture2D.h"
#include "GameObject.h"
#include <vector>

struct Particle
{
	glm::vec2 position, velocity;
	glm::vec4 color;
	GLfloat life;

	Particle() :position(0.0f), velocity(0.0f), color(1.0f), life(0.0f) {}
};

class ParticleGenerator
{
public:
	ParticleGenerator(Shader shader, Texture2D texture, GLuint amount);
	void Update(GLfloat dt, GameObject& object, GLuint newParticles, glm::vec2 offset = glm::vec2(0.0f, 0.0f));
	void Draw();
private:
	std::vector<Particle> particles;
	GLuint amount;
	Shader shader;
	Texture2D texture;
	GLuint VAO;
	void Init();
	GLuint FirstUnusedParticle();
	void RespawnParticle(Particle& particle, GameObject& object, glm::vec2 offset = glm::vec2(0.0f, 0.0f));
};

ParticleGenerator.cpp:

#include "ParticleGenerator.h"

ParticleGenerator::ParticleGenerator(Shader shader, Texture2D texture, GLuint amount) : shader(shader), texture(texture), amount(amount)
{
	this->Init();
}

void ParticleGenerator::Update(GLfloat dt, GameObject& object, GLuint newParticles, glm::vec2 offset)
{
	// Add new particles 
	for (GLuint i = 0; i < newParticles; ++i)
	{
		int unusedParticle = this->FirstUnusedParticle();
		this->RespawnParticle(this->particles[unusedParticle], object, offset);
	}
	// Update all particles
	for (GLuint i = 0; i < this->amount; ++i)
	{
		Particle& p = this->particles[i];
		p.life -= dt; // reduce life
		if (p.life > 0.0f)
		{	// particle is alive, thus update
			p.position -= p.velocity * dt;
			p.color.a -= dt * 2.5;
		}
	}
}

//render all particles
void ParticleGenerator::Draw()
{
	// Use additive blending to give it a 'glow' effect
	glBlendFunc(GL_SRC_ALPHA, GL_ONE);
	this->shader.Use();
	for (Particle particle : this->particles)
	{
		if (particle.life > 0.0f)
		{
			this->shader.SetVector2f("offset", particle.position);
			this->shader.SetVector4f("color", particle.color);
			this->texture.Bind();
			glBindVertexArray(this->VAO);
			glDrawArrays(GL_TRIANGLES, 0, 6);
			glBindVertexArray(0);
		}
	}
	// Don't forget to reset to default blending mode
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}

void ParticleGenerator::Init()
{
	//set up mesh and attribute properties
	GLuint VBO;
	GLfloat particleQuad[] =
	{
		0.0f, 1.0f, 0.0f, 1.0f,
		1.0f, 0.0f, 1.0f, 0.0f,
		0.0f, 0.0f, 0.0f, 0.0f,

		0.0f, 1.0f, 0.0f, 1.0f,
		1.0f, 1.0f, 1.0f, 1.0f,
		1.0f, 0.0f, 1.0f, 0.0f
	};
	glGenVertexArrays(1, &this->VAO);
	glGenBuffers(1, &VBO);
	glBindVertexArray(this->VAO);
	//fill mesh buffer
	glBindBuffer(GL_ARRAY_BUFFER, VBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(particleQuad), particleQuad, GL_STATIC_DRAW);
	//set mesh attributes
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (GLvoid*)0);
	glBindVertexArray(0);

	//create this->amount default particle instances
	for (GLuint i = 0; i < this->amount; i++)
	{
		this->particles.push_back(Particle());
	}
}

//stores the index of the last particle used 
GLuint lastUsedParticle = 0;
GLuint ParticleGenerator::FirstUnusedParticle()
{
	//First search from last used particle,this will usually return almost instantly
	for (GLuint i = lastUsedParticle; i < this->amount; i++)
	{
		if (this->particles[i].life <= 0.0f)
		{
			lastUsedParticle = i;
			return i;
		}
	}

	//otherwise,do a linear search
	for (GLuint i = 0; i < lastUsedParticle; i++)
	{
		if (this->particles[i].life <= 0.0f)
		{
			lastUsedParticle = i;
			return i;
		}
	}

	//all particles are taken,override the first one
	lastUsedParticle = 0;
	return 0;
}

void ParticleGenerator::RespawnParticle(Particle& particle, GameObject& object, glm::vec2 offset)
{
	GLfloat random =((rand() % 100) - 50) / 10.0f;
	GLfloat rColor = 0.5 + ((rand() % 100) / 100.0f);
	particle.position = object.position + random + offset;
	particle.color = glm::vec4(rColor, rColor, rColor, 1.0f);
	particle.life = 1.0f;
	particle.velocity = object.velocity * 0.1f;
}

Game.cpp:

#include "ResourceManager.h"
#include "Game.h"
#include "SpriteRenderer.h"
#include "BallObject.h"
#include "ParticleGenerator.h"

SpriteRenderer* renderer;
GameObject* player;
BallObject* ball;
ParticleGenerator* particles;

Game::Game(GLuint w, GLuint h) :state(GAME_ACTIVE), keys(), width(w), height(h) {}

Game::~Game()
{
	delete renderer;
	delete player;
	delete ball;
	delete particles;
}

void Game::Init()
{
	//load shader
	ResourceManager::LoadShader("Breakout/Shaders/Sprite.vs", "Breakout/Shaders/Sprite.fs", nullptr, "sprite");
	ResourceManager::LoadShader("Breakout/Shaders/Particle.vs", "Breakout/Shaders/Particle.fs", nullptr, "particle");
	//config shader
	glm::mat4 projection = glm::ortho(0.0f, static_cast<GLfloat>(this->width), static_cast<GLfloat>(this->height), 0.0f, -1.0f, 1.0f);
	ResourceManager::GetShader("sprite").Use().SetInteger("image", 0);
	ResourceManager::GetShader("sprite").SetMatrix4("projection", projection);
	ResourceManager::GetShader("particle").Use().SetInteger("sprite", 0);
	ResourceManager::GetShader("particle").SetMatrix4("projection", projection);
	//load texture
	ResourceManager::LoadTexture("Breakout/Images/background.jpg", GL_TRUE, "background");
	ResourceManager::LoadTexture("Breakout/Images/block.png", GL_FALSE, "block");
	ResourceManager::LoadTexture("Breakout/Images/block_solid.png", GL_FALSE, "block_solid");
	ResourceManager::LoadTexture("Breakout/paddle.png", true, "paddle");//player
	ResourceManager::LoadTexture("Breakout/face.png", true, "ball");//ball
	ResourceManager::LoadTexture("Breakout/particle.png", true, "particle");//particle
	//setup render control
	renderer = new SpriteRenderer(ResourceManager::GetShader("sprite"));
	particles = new ParticleGenerator(ResourceManager::GetShader("particle"), ResourceManager::GetTexture("particle"), 500);
	//load levels
	GameLevel one; one.Load("Breakout/Levels/1.lvl", this->width, this->height * 0.5);
	GameLevel two; two.Load("Breakout/Levels/2.lvl", this->width, this->height * 0.5);
	GameLevel three; three.Load("Breakout/Levels/3.lvl", this->width, this->height * 0.5);
	GameLevel four; four.Load("Breakout/Levels/4.lvl", this->width, this->height * 0.5);

	this->levels.push_back(one);
	this->levels.push_back(two);
	this->levels.push_back(three);
	this->levels.push_back(four);
	this->currentLevel = 0;

	//player init
	glm::vec2 playerPos = glm::vec2(this->width / 2 - PLAYER_SIZE.x / 2, this->height - PLAYER_SIZE.y);
	player = new GameObject(playerPos, PLAYER_SIZE, ResourceManager::GetTexture("paddle"));

	//ball init    原点位置是左上角
	glm::vec2 ballPos = playerPos + glm::vec2(PLAYER_SIZE.x / 2 - BALL_RADIUS, -BALL_RADIUS * 2);
	ball = new BallObject(ballPos, BALL_RADIUS, INITIAL_BALL_VELOCITY, ResourceManager::GetTexture("ball"));

	particle
	//particles = new ParticleGenerator(ResourceManager::GetShader("particle"), ResourceManager::GetTexture("particle"), 500);
	//glGetError();
}

void Game::ProcessInput(GLfloat dt)
{
	if (this->state == GAME_ACTIVE)
	{
		GLfloat velocity = PLAYER_VELOCITY * dt;
		//移动挡板
		if (this->keys[GLFW_KEY_A])
		{
			if (player->position.x >= 0)
			{
				player->position.x -= velocity;

				if (ball->stuck)
					ball->position.x -= velocity;
			}
		}
		if (this->keys[GLFW_KEY_D])
		{
			if (player->position.x <= this->width - player->size.x)
			{
				player->position.x += velocity;
				if (ball->stuck)
					ball->position.x += velocity;
			}
		}
		if (this->keys[GLFW_KEY_SPACE])
			ball->stuck = false;
	}
}

void Game::Update(GLfloat dt)
{
	//update ball
	ball->Move(dt, this->width);

	//collision detection
	this->DoCollisions();

	//particle
	particles->Update(dt, *ball, 2, glm::vec2(ball->radius / 2));

	//球是否接触底部边界？
	if (ball->position.y >= this->height)
	{
		this->ResetLevel();
		this->ResetPlayer();
	}
}

void Game::Render()
{
	if (this->state == GAME_ACTIVE)
	{
		//绘制背景
		renderer->DrawSprite(ResourceManager::GetTexture("background"), glm::vec2(0, 0), glm::vec2(this->width, this->height), 0.0f);

		//绘制关卡
		this->levels[this->currentLevel].Draw(*renderer);

		//绘制玩家挡板
		player->Draw(*renderer);

		//绘制粒子
		particles->Draw();

		//绘制球
		ball->Draw(*renderer);
	}
}

Direction VectorDirection(glm::vec2 target)
{
	glm::vec2 compass[] =
	{
		glm::vec2(0.0f,1.0f),
		glm::vec2(1.0f,0.0f),
		glm::vec2(0.0f,-1.0f),
		glm::vec2(-1.0f,0.0f),
	};

	GLfloat max = 0.0f;
	GLuint bestMatch = -1;
	for (GLuint i = 0; i < 4; i++)
	{
		GLfloat dot = glm::dot(glm::normalize(target), compass[i]);
		if (dot > max)
		{
			max = dot;
			bestMatch = i;
		}
	}
	return (Direction)bestMatch;
}

//碰撞检测：：AABB
GLboolean CheckCollision(GameObject& one, GameObject& two) // AABB - AABB collision
{
	// x轴方向碰撞？
	bool collisionX = one.position.x + one.size.x >= two.position.x &&
		two.position.x + two.size.x >= one.position.x;
	// y轴方向碰撞？
	bool collisionY = one.position.y + one.size.y >= two.position.y &&
		two.position.y + two.size.y >= one.position.y;
	// 只有两个轴向都有碰撞时才碰撞
	return collisionX && collisionY;
}

//碰撞检测：方形和圆形
Collision CheckCollision(BallObject& one, GameObject& two) // AABB - Circle collision
{
	//获取圆的中心
	glm::vec2 center(one.position + one.radius);
	//计算AABB的信息（中心，半边长）
	glm::vec2 aabb_half_extents(two.size.x / 2, two.size.y / 2);
	glm::vec2 aabb_center(two.position.x + aabb_half_extents.x, two.position.y + aabb_half_extents.y);
	//获取两个中心的差矢量
	glm::vec2 difference = center - aabb_center;
	glm::vec2 clamped = glm::clamp(difference, -aabb_half_extents, aabb_half_extents);
	//AABB_center 加上clampled这样就得到了碰撞箱上距离最近点closest
	glm::vec2 closest = aabb_center + clamped;
	//获得圆心center和最近点closest的矢量，并判断是否length<=radius
	difference = closest - center;
	if (glm::length(difference) < one.radius)
		return std::make_tuple(GL_TRUE, VectorDirection(difference), difference);
	else
		return std::make_tuple(GL_FALSE, UP, glm::vec2(0, 0));
}

void Game::DoCollisions()
{
	for (GameObject& box : this->levels[this->currentLevel].bricks)
	{
		if (!box.destroyed)
		{
			Collision collision = CheckCollision(*ball, box);
			if (std::get<0>(collision))
			{
				if (!box.isSoild)
					box.destroyed = GL_TRUE;
				//碰撞处理
				Direction dir = std::get<1>(collision);
				glm::vec2 diff_vector = std::get<2>(collision);
				if (dir == LEFT || dir == RIGHT)
				{
					ball->velocity.x = -ball->velocity.x;//反转水平速度
					//重定位
					GLfloat penetration = ball->radius - std::abs(diff_vector.x);
					if (dir == LEFT)
						ball->position.x += penetration;//球右移
					else
						ball->position.x -= penetration;//球左移
				}
				else//垂直方形碰撞
				{
					ball->velocity.y = -ball->velocity.y;//反转垂直速度
					//重定位
					GLfloat penetration = ball->radius - std::abs(diff_vector.y);
					if (dir == UP)
						ball->position.y -= penetration;//球上移
					else
						ball->position.y += penetration;//球下移						
				}
			}

			//玩家--球碰撞
			Collision result = CheckCollision(*ball, *player);
			if (!ball->stuck && std::get<0>(result))
			{
				//检查碰到了挡板的哪个位置，并根据碰撞到哪个位置改变速度
				GLfloat centerBoard = player->position.x + player->size.x / 2;
				GLfloat distance = (ball->position.x + ball->radius) - centerBoard;
				GLfloat percentage = distance / (player->size.x / 2);
				//依据结果移动
				GLfloat strength = 2.0f;
				glm::vec2 oldVelocity = ball->velocity;
				ball->velocity.x = INITIAL_BALL_VELOCITY.x * percentage * strength;
				//ball->velocity.y = -ball->velocity.y;
				//解决粘板问题：保证最后的Y方向始终向上
				ball->velocity.y = -1 * abs(ball->velocity.y);
				//新的速度：新的归一化方向*原来速度的大小
				ball->velocity = glm::normalize(ball->velocity) * glm::length(oldVelocity);
			}
		}
	}
}

void Game::ResetLevel()
{
	if (this->currentLevel == 0)
		this->levels[0].Load("Breakout/Levels/1.lvl", this->width, this->height * 0.5f);
	else if (this->currentLevel == 1)
		this->levels[1].Load("Breakout/Levels/2.lvl", this->width, this->height * 0.5f);
	else if (this->currentLevel == 2)
		this->levels[1].Load("Breakout/Levels/3.lvl", this->width, this->height * 0.5f);
	else if (this->currentLevel == 3)
		this->levels[1].Load("Breakout/Levels/4.lvl", this->width, this->height * 0.5f);
}

void Game::ResetPlayer()
{
	player->size = PLAYER_SIZE;
	player->position = glm::vec2(this->width / 2 - PLAYER_SIZE.x / 2, this->height - PLAYER_SIZE.y);
	ball->Reset(player->position + glm::vec2(PLAYER_SIZE.x / 2 - ball->radius, -(BALL_RADIUS * 2)), INITIAL_BALL_VELOCITY);
}

粒子顶点着色器：

#version 330 core
layout (location = 0) in vec4 vertex; // <vec2 position, vec2 texCoords>

out vec2 TexCoords;
out vec4 ParticleColor;

uniform mat4 projection;
uniform vec2 offset;
uniform vec4 color;

void main()
{
    float scale = 10.0f;
    TexCoords = vertex.zw;
    ParticleColor = color;
    gl_Position = projection * vec4((vertex.xy * scale) + offset, 0.0, 1.0);
}

粒子片元着色器：

#version 330 core
in vec2 TexCoords;
in vec4 ParticleColor;
out vec4 color;

uniform sampler2D sprite;

void main()
{
    color = (texture(sprite, TexCoords) * ParticleColor);
}```