IT博客汇 | [原]OpenGL进阶(十九)

[原]OpenGL进阶(十九) - 多光源

qp120291570发表于 2015-01-16 11:22:56

从光说起

先看一段wiki中对光的定义

光是一种人类眼睛可以见的电磁波（可见光谱），视知觉就是对于光的知觉[1]。光只是电磁波谱上的某一段频谱，一般是定义为波长介于400至700纳米（nm）之间的电磁波，也就是波长比紫外线长，比红外线短的电磁波。有些资料来源定义的可见光的波长范围也有不同，较窄的有介于420至680纳米，较宽的有介于380至800纳米。

光既是一种高频的电磁波，又是一种由称为光子的基本粒子组成的粒子流。因此光同时具有粒子性与波动性，或者说光具有“波粒二象性”。

按波动理论来解释，不同颜色的光就是不同波长的电磁波。

光的衰减（Attenuation）

任何点光源的光照亮度随着距离增加会迅速衰减。这个就叫光的衰减。

不同波长的光有不同的衰减方式，还有就是灯光所处的环境，比如是否有雾霾，下面是常见的几种衰减模型。

这里实现一个衰减的类，作为灯光的成员

#pragma once
class Attenuation
{
public:
	Attenuation(float range, float constant, float linear, float quadratic) :
		m_range(range),
		m_constant(constant),
		m_linear(linear),
		m_quadratic(quadratic) {}

	inline float getRange() const { return m_range; }
	inline float getConstant() const { return m_constant; }
	inline float getLinear()   const { return m_linear; }
	inline float getQuadratic() const { return m_quadratic; }

private:
	float m_constant;
	float m_linear;
	float m_quadratic;
	float m_range;
};

Attenuation类有4个成员后面三项是常量项，线性项还有二次项，最后的衰减率的计算是由下面的公式确定的，Distance表示光源到点的距离。

attenuation = Constant + Linear * Distance + Quadratic * Distance ^ 2

第一个成员表示光源照亮的范围，下面有一个表可以用来查询四者之间的关系

当你选定了一个Rang的时候，你就可以找到对应的constant，linear 和 quadratic。

Constant 越趋近于0，灯光就越亮，反之越暗。

Linear越大，灯光衰减得就越快。不建议改变Quadratic值或者减少Linear的值，这样做需要重新计算Range.

减少Range值可以提升渲染的速度，但是减少得太多，在游戏中可能会造成灯光效果的突变。

点光源

首先创建一个BaseLight类，作为各种灯光的基类

#pragma once
#include "common.h"

class BaseLight
{
public:
	BaseLight(const glm::vec3& color, const glm::vec3& pos,  float intensity) :
		m_color(color),
		m_pos(pos),
		m_intensity(intensity) {}

	inline glm::vec3 getPos() const  {return m_pos;}
	inline float getIntensity() { return m_intensity; }
	inline glm::vec3 getColor() { return m_color; }

private:
	glm::vec3    m_color;
	glm::vec3 m_pos;
	float      m_intensity;
};

注意，很多教程上光的属性有ambient，diffuse，specular之类，按照前面的原理，这都是不科学的，包括材质的Ambient，其实环境光应该是一个全局常量，所以材质也只能diffuse, specular. 插一段StackOverflow上的回答。

这里基础灯光只有三个成员，颜色，位置，强度。

点光源的类

#pragma once
#include "baselight.h"
#include "attenuation.h"
class PointLight :public BaseLight
{
public:
public:
	PointLight(const glm::vec3& color = glm::vec3(0, 0, 0), const glm::vec3& pos = glm::vec3(0, 0, 0), const float intensity = 1.0, const Attenuation& atten = Attenuation()):
	BaseLight(color,pos,intensity),m_attenuation(atten){}

	inline const Attenuation& getAttenuation() const { return m_attenuation; }

private:
	Attenuation m_attenuation;
};

灯光的初始化，So easy.

	pointLight = new PointLight(glm::vec3(0, 1, 0), glm::vec3(3, 3, 3), 1.8, Attenuation(20, 1.0, 0.22, 0.20));

给shader传参数

	prog.setUniform("pointLight.pos", pointLight->getPos());
	prog.setUniform("pointLight.color", pointLight->getColor());
	prog.setUniform("pointLight.intensity", pointLight->getIntensity());
	prog.setUniform("pointLight.constant", pointLight->getAttenuation().getConstant());
	prog.setUniform("pointLight.linear", pointLight->getAttenuation().getLinear());
	prog.setUniform("pointLight.quadratic", pointLight->getAttenuation().getQuadratic());
	prog.setUniform("pointLight.range", pointLight->getAttenuation().getRange());

接下来就是shader了

vertex shader 就是传个值。

#version 400
layout (location = 0) in vec3 VertexPosition;  
layout (location = 1) in vec2 VertexUv;  
layout (location = 2) in vec3 VertexNormal;  

uniform mat4 MVP;
 
out vec3 position;  
out vec3 normal;  

void main()
{
	normal = VertexNormal;
	position =  VertexPosition;
	gl_Position = MVP * vec4( VertexPosition, 1.0);
}

fragment shader也就是三板斧，ambient，diffuse，specular，具体计算看Code

#version 400

struct PointLight
{
	float range;
	vec3 pos;
	vec3 color;
	float intensity;
	float constant;
    float linear;
    float quadratic;  
};

struct MaterialInfo{  
    vec3 diffuse;  
    vec3 specular;  
    float shininess;  
};  
uniform vec3 ambient; 
uniform PointLight pointLight;
uniform MaterialInfo materialInfo;
uniform vec3 cameraPosition;

in vec3 position;
in vec3 normal;
out vec4 finalColor;

vec3 calculatePointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
	vec3 lightDir = normalize(light.pos - fragPos);
	//ambient
	vec3 ambFactor = ambient;
	// Diffuse shading
	float diffFactor = max(dot(normal, lightDir), 0.0) * light.intensity ;
	// Specular shading
	vec3 reflectDir = normalize(reflect(-lightDir, normal));
	float specFactor = pow(max(dot(viewDir, reflectDir), 0.0), materialInfo.shininess) * light.intensity;
	// Attenuation
    float distance = length(light.pos - fragPos);
	float attenuation = 1.0f;
	if(distance < light.range)
	{
	    attenuation = 1.0f / (light.constant + light.linear * distance + 
  			    light.quadratic * (distance * distance));  
	}
	
	vec3 ambientColor = ambFactor;
	vec3 diffuseColor = diffFactor * materialInfo.diffuse * light.color;
	vec3 specularColor = specFactor * materialInfo.specular * light.color ;
	return ambientColor + attenuation * (diffuseColor + specularColor);
}


void main(void)
{
	vec3 totalLight = vec3(0,0,0);
	vec3 norm = normalize(normal);
	vec3 viewDir = normalize(cameraPosition - position);
	totalLight += calculatePointLight(pointLight, normal, position, viewDir);
	finalColor = vec4(totalLight, 1.0);
	return;
}

运行结果

多光源

先看下最终的效果,是不是有点炫酷！？

整体的思路是：创建3个点光源，然后传到把点光源的信息都传递进去，开一个定时器，不断更新光源的位置，再更新shader数据，最后再绘制。

首先创建一个简单的场景类，注意这个类是要继承QObject的，因为要用到Qt的Signal/Slot机制。

#ifndef SCENE_H
#define SCENE_H
#include 
#include 
#include 
#include 
#include "light/pointlight.h"
#include "shader/shaderprogram.h"
#include 

class Scene : public QObject
{
	Q_OBJECT

public:
	Scene(QObject *parent = 0);
	~Scene();
	void addLight(PointLight* pLight);
	void setShader(ShaderProgram *pShader);
	void setUniform();

private:

	std::vector pointLights;
	ShaderProgram *shaderProgram;
	QTimer *updateTimer;

private slots:
	void updateLight();
	
signals:
	void updateScene();
};

#endif // SCENE_H

接下来是cpp的实现

#include "scene.h"

Scene::Scene(QObject *parent)
	: QObject(parent)
{
	updateTimer = new QTimer();
	updateTimer->setInterval(30);
	connect(updateTimer, SIGNAL(timeout()), this, SLOT(updateLight()));
	updateTimer->start();
}


Scene::~Scene()
{
	for (int i = 0; i < pointLights.size(); i++)
	{
		delete pointLights[i];
	}
}

void Scene::addLight(PointLight* pLight)
{
	pointLights.push_back(pLight);
}

void Scene::setUniform()
{
	char tmp[100];
	int count = static_cast(pointLights.size());
	shaderProgram->setUniform("pointLightCount", count);
	for (int i = 0; i < count; i++)
	{
		sprintf(tmp, "pointLights[%d].pos", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getPos());
		sprintf(tmp, "pointLights[%d].color", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getColor());
		sprintf(tmp, "pointLights[%d].intensity", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getIntensity());
		sprintf(tmp, "pointLights[%d].constant", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getAttenuation().getConstant());
		sprintf(tmp, "pointLights[%d].linear", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getAttenuation().getLinear());
		sprintf(tmp, "pointLights[%d].quadratic", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getAttenuation().getQuadratic());
		sprintf(tmp, "pointLights[%d].range", i);
		shaderProgram->setUniform(tmp, pointLights[i]->getAttenuation().getRange());
	}

}

void Scene::setShader(ShaderProgram *pShader)
{
	shaderProgram = pShader;
}

void Scene::updateLight()
{
	glm::mat4 transMatrix = glm::translate(glm::mat4(1.0f), glm::vec3(0, 2, 0));
	glm::mat4 rotationX = glm::rotate(transMatrix, 0.1f, glm::vec3(1, 0, 0));
	glm::mat4 rotationY = glm::rotate(transMatrix, 0.1f, glm::vec3(0, 1, 0));
	glm::mat4 rotationZ = glm::rotate(transMatrix, 0.1f, glm::vec3(0, 0, 1));

	glm::vec4  newPos = glm::vec4(pointLights[0]->getPos(), 1.0f) * rotationX;
	pointLights[0]->setPos(glm::vec3(newPos));

	newPos = glm::vec4(pointLights[1]->getPos(), 1.0f) * rotationY;
	pointLights[1]->setPos(glm::vec3(newPos));

	newPos = glm::vec4(pointLights[2]->getPos(), 1.0f) * rotationZ;
	pointLights[2]->setPos(glm::vec3(newPos));

	this->setUniform();
	emit updateScene();
}

解释两个函数，

setUniform

向shader中传递当前灯光的参数。

updateLight

更新灯光的位置，不知道咋转的回去看线性代数。想偷懒的看这个 Real-Time Rendering (2) - 变换和矩阵（Transforms and Matrics）。

更新完之后调用setUniform传递参数。

最后看他们的初始化

void MainWidget::initScene()
{
	// Calculate aspect ratio
	float aspect = float(width()) / float(height() ? height() : 1);
	const float zNear = 0.01, zFar = 100.0, fov = 45.0;

	// Set projection
	mainCamera = new Camera(glm::vec3(0, 5, 10), glm::vec3(0, 3, 0), glm::vec3(0.0, 1.0, 0.0));
	mainCamera->setPerspectiveParameter(fov, aspect, zNear, zFar);
	modelMatrix = glm::mat4(1.0f);

	scene = new Scene();
	connect(scene, SIGNAL(updateScene()), this, SLOT(update()));
	scene->setShader(&prog;);

	PointLight *pointLight1 = new PointLight(glm::vec3(0, 1, 0), glm::vec3(0, 2, 3), 1.8, Attenuation(20, 0.1, 0.22, 0.20));
	PointLight *pointLight2 = new PointLight(glm::vec3(1, 0, 0), glm::vec3(3, 2, 0), 1.8, Attenuation(20, 0.1, 0.22, 0.20));
	PointLight *pointLight3 = new PointLight(glm::vec3(0, 0, 1), glm::vec3(-3, 2, 0), 1.8, Attenuation(20, 0.1, 0.22, 0.20));

	scene->addLight(pointLight1);
	scene->addLight(pointLight2);
	scene->addLight(pointLight3);

	compileShader();
	setUniform();
	objModel.loadFromFile("../Assets/model/bunny.obj");
	objModel.setShader(prog);
}

Fragment Shader需要做一些改变

#version 400
const int MAX_POINT_LIGHTS = 5;                                                       

struct PointLight
{
	float range;
	vec3 pos;
	vec3 color;
	float intensity;
	float constant;
    float linear;
    float quadratic;  
};

struct MaterialInfo{  
    vec3 diffuse;  
    vec3 specular;  
    float shininess;  
};  

uniform vec3 ambient; 

uniform int pointLightCount; 
uniform PointLight pointLights[MAX_POINT_LIGHTS];
uniform MaterialInfo materialInfo;
uniform vec3 cameraPosition;

in vec3 position;
in vec3 normal;
out vec4 finalColor;

vec3 calculatePointLight(PointLight light, vec3 normal, vec3 fragPos, vec3 viewDir)
{
	vec3 lightDir = normalize(light.pos - fragPos);
	//ambient
	vec3 ambFactor = ambient;
	// Diffuse shading
	float diffFactor = max(dot(normal, lightDir), 0.0) * light.intensity ;
	// Specular shading
	vec3 reflectDir = normalize(reflect(-lightDir, normal));
	float specFactor = pow(max(dot(viewDir, reflectDir), 0.0), materialInfo.shininess) * light.intensity;
	// Attenuation
    float distance = length(light.pos - fragPos);
	float attenuation = 1.0f;
	if(distance < light.range)
	{
	    attenuation = 1.0f / (light.constant + light.linear * distance + 
  			    light.quadratic * (distance * distance));  
	}
	
	vec3 ambientColor = ambFactor;
	vec3 diffuseColor = diffFactor * materialInfo.diffuse * light.color;
	vec3 specularColor = specFactor * materialInfo.specular * light.color ;
	//return ambientColor + attenuation * (diffuseColor + specularColor);
	return attenuation * (diffuseColor + specularColor);
}


void main(void)
{
	vec3 totalLight = vec3(0,0,0);
	vec3 norm = normalize(normal);
	vec3 viewDir = normalize(cameraPosition - position);
	for(int i = 0; i < pointLightCount; i++)
	{
		totalLight += calculatePointLight(pointLights[i], normal, position, viewDir);
	}
	finalColor = vec4(totalLight, 1.0);
	return;
}

打完收工。

参考

Point Light Attenuation - http://www.ogre3d.org/tikiwiki/tiki-index.php?page=-Point+Light+Attenuation

Multiple lights - http://www.learnopengl.com/#!Lighting/Multiple-lights

Modern OpenGL 07 – More Lighting: Ambient, Specular, Attenuation, Gamma - http://www.tomdalling.com/blog/modern-opengl/07-more-lighting-ambient-specular-attenuation-gamma/

BennyQBD/3DEngineCpp - https://github.com/BennyQBD/3DEngineCpp