Hands-on C++ Game Animation Programming阅读笔记（四）
Chapter 6: Building an Abstract Renderer
In order to avoid getting caught up in any specific graphics APIs, in this chapter, you will build an abstraction layer on top of OpenGL.
本章没啥重点内容，就是OpenGL的那些东西，稍微新一点的几个OpenGL的api，之前没使用过：
glGetActiveUniformglGetActiveAttrib
Shader类
定义Shader头文件
头文件如下：
#ifndef _H_SHADER_
#define _H_SHADER_
#include <map>
#include <string>
class Shader
{
private:
unsigned int mHandle;
std::map<std::string, unsigned int> mAttributes;
std::map<std::string, unsigned int> mUniforms;
private:
std::string ReadFile(const std::string& path);
// compile shader source code and return an OpenGL handle.
unsigned int CompileVertexShader(const std::string& vertex);
unsigned int CompileFragmentShader(const std::string& fragment);
// link two shaders into a shader program
bool LinkShaders(unsigned int vertex, unsigned int fragment);
// populate有填充的意思, 这俩函数是取OpenGL里的Attribs和Uniforms, 存到两个map里面
void PopulateAttributes();
void PopulateUniforms();
private:
// 通过私有的copy ctor和copy assignment operator禁止Shader对象的拷贝
Shader(const Shader&);
Shader& operator=(const Shader&);
public:
Shader();
// The overload constructor will call the Load method, which loads shaders from files and compiles them.
Shader(const std::string& vertex, const std::string& fragment);
// The destructor will release the OpenGL shader handle that the Shader class is holding on
~Shader();
void Load(const std::string& vertex, const std::string& fragment);
// Before a shader is used, it will need to be bound with the Bind function.
void Bind();
void UnBind();
// perform lookups in the appropriate dictionaries
unsigned int GetAttribute(const std::string& name);
unsigned int GetUniform(const std::string& name);
// returns the shader's OpenGL handle
unsigned int GetHandle();
};
#endif
Get All Uniforms And Attributes
一个Shader对象代表一个Shader Program，读取文件、编译和Link Shader都是我做过好多次的东西，这次唯一没做过的就是获取一个Shader Program的所有Uniforms和Attributes，存到Shader的两个map里，Shader的uniforms我比较清楚，而Attributes应该是使用glVertexArrayAttrib分配的顶点属性。
相关部分的代码如下：
// 准确的说, 这个类应该叫OpenGLShader
class Shader
{
std::map<std::string, unsigned int> mAttributes;
std::map<std::string, unsigned int> mUniforms;
// perform lookups in the appropriate dictionaries
unsigned int GetAttribute(const std::string& name)
{
// 遍历map. 找到命名为name的attribute对应的id
std::map<std::string, unsigned int>::iterator it = mAttributes.find(name);
if (it == mAttributes.end())
{
std::cout << "Retrieving bad attribute index: " << name << "\n";
return 0;
}
return it->second;
}
unsigned int GetUniform(const std::string& name)
{
// 遍历map. 找到命名为name的uniform对应的id
std::map<std::string, unsigned int>::iterator it = mUniforms.find(name);
if (it == mUniforms.end())
{
std::cout << "Retrieving bad uniform index: " << name << "\n";
return 0;
}
return it->second;
}
// 收集Shader Program里的active attribs, 加入到map里
void PopulateAttributes()
{
int count = -1;
int length;
char name[128];
int size;
GLenum type;
glUseProgram(mHandle);
// glGetProgramiv用于获取Shader Program的信息, 第二个参数是个枚举，可以为：
// GL_DELETE_STATUS, GL_LINK_STATUS, GL_VALIDATE_STATUS, GL_INFO_LOG_LENGTH,
// GL_ATTACHED_SHADERS, GL_ACTIVE_ATTRIBUTES, GL_ACTIVE_ATTRIBUTE_MAX_LENGTH,
// GL_ACTIVE_UNIFORMS, GL_ACTIVE_UNIFORM_MAX_LENGTH.
// 第三个参数是一个int*, 其含义根据输入的枚举不同而不一样, 这里的意思是active attribs的个数
glGetProgramiv(mHandle, GL_ACTIVE_ATTRIBUTES, &count);
// 遍历每一个顶点属性
for (int i = 0; i < count; ++i)
{
memset(name, 0, sizeof(char) * 128);
// 获取shader program的第i个active attrib的length、size、type和name
glGetActiveAttrib(mHandle, (GLuint)i, 128, &length, &size, &type, name);
// 获取对应attrib的id, 存到map里
int attrib = glGetAttribLocation(mHandle, name);
if (attrib >= 0)
mAttributes[name] = attrib;
}
glUseProgram(0);
}
// 收集Shader Program里的active uniforms, 加入到map里
void PopulateUniforms()
{
int count = -1;
int length;
char name[128];
int size;
GLenum type;
char testName[256];
glUseProgram(mHandle);
// GL_ACTIVE_UNIFORMS
glGetProgramiv(mHandle, GL_ACTIVE_UNIFORMS, &count);
// 遍历每个active uniform
for (int i = 0; i < count; ++i)
{
memset(name, 0, sizeof(char) * 128);
glGetActiveUniform(mHandle, (GLuint)i, 128, &length, &size, &type, name);
int uniform = glGetUniformLocation(mHandle, name);// Get Handle in OpenGL
// 额外加了个对uniform的处理
if (uniform >= 0)
{
std::string uniformName = name;
// 通过uniform的名字, 判断它是不是uniform array
std::size_t found = uniformName.find('[');
// 如果uniform是数组
if (found != std::string::npos)
{
// 清除string后面的'['开始的内容
uniformName.erase(uniformName.begin() + found, uniformName.end());
// Populate subscripted names too
unsigned int uniformIndex = 0;
// 以uniform的名字开始, 往后搜寻同一数组内的uniform
while (true)
{
memset(testName, 0, sizeof(char) * 256);
// 拼接新的字符串: uniformName[uniformIndex], 存到testName里
sprintf(testName, "%s[%d]", uniformName.c_str(), uniformIndex++);
int uniformLocation = glGetUniformLocation(mHandle, testName);
if (uniformLocation < 0)
break;
// 加入到mUniforms里, 这里的testName是带[]序号的
mUniforms[testName] = uniformLocation;
}
}
// 把不带'[]'的单纯的数组的名字, 或者uniform不为数组时的单独的uniform, 存入map
// 也就是说, 对于m个元素的uniform数组, map里存了m+1个相关的pair
mUniforms[uniformName] = uniform;
}
}
glUseProgram(0);
}
}
cpp文件
// 严格意义上说, 这里的Shader应该叫OpenGLShader, 因为这个cpp里用到了很多OpenGL的api, 并不是abstract的
#define _CRT_SECURE_NO_WARNINGS
#include "Shader.h"
#include "glad.h"
#include <fstream>
#include <sstream>
#include <iostream>
Shader::Shader()
{
mHandle = glCreateProgram();
}
Shader::Shader(const std::string& vertex, const std::string& fragment)
{
mHandle = glCreateProgram();
Load(vertex, fragment);
}
Shader::~Shader()
{
glDeleteProgram(mHandle);
}
// 利用ifstream和stringstream读取path文件里的内容, 老一套了
std::string Shader::ReadFile(const std::string& path)
{
std::ifstream file;
file.open(path);
std::stringstream contents;
contents << file.rdbuf();
file.close();
return contents.str();
}
unsigned int Shader::CompileVertexShader(const std::string& vertex)
{
unsigned int v_shader = glCreateShader(GL_VERTEX_SHADER);
const char* v_source = vertex.c_str();
glShaderSource(v_shader, 1, &v_source, NULL);
glCompileShader(v_shader);
int success = 0;
glGetShaderiv(v_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
char infoLog[512];
glGetShaderInfoLog(v_shader, 512, NULL, infoLog);
std::cout << "ERROR: Vertex compilation failed.\n";
std::cout << "\t" << infoLog << "\n";
glDeleteShader(v_shader);
return 0;
};
return v_shader;
}
//
unsigned int Shader::CompileFragmentShader(const std::string& fragment)
{
unsigned int f_shader = glCreateShader(GL_FRAGMENT_SHADER);
const char* f_source = fragment.c_str();
glShaderSource(f_shader, 1, &f_source, NULL);
glCompileShader(f_shader);
int success = 0;
// Check for errors with glGetShaderiv
glGetShaderiv(f_shader, GL_COMPILE_STATUS, &success);
if (!success)
{
char infoLog[512];
glGetShaderInfoLog(f_shader, 512, NULL, infoLog);
std::cout << "ERROR: Fragment compilation failed.\n";
std::cout << "\t" << infoLog << "\n";
glDeleteShader(f_shader);
return 0;
};
return f_shader;
}
bool Shader::LinkShaders(unsigned int vertex, unsigned int fragment)
{
glAttachShader(mHandle, vertex);
glAttachShader(mHandle, fragment);
glLinkProgram(mHandle);
int success = 0;
glGetProgramiv(mHandle, GL_LINK_STATUS, &success);
if (!success)
{
char infoLog[512];
glGetProgramInfoLog(mHandle, 512, NULL, infoLog);
std::cout << "ERROR: Shader linking failed.\n";
std::cout << "\t" << infoLog << "\n";
glDeleteShader(vertex);
glDeleteShader(fragment);
return false;
}
glDeleteShader(vertex);
glDeleteShader(fragment);
return true;
}
void Shader::PopulateAttributes()
{
int count = -1;
int length;
char name[128];
int size;
GLenum type;
glUseProgram(mHandle);
glGetProgramiv(mHandle, GL_ACTIVE_ATTRIBUTES, &count);
for (int i = 0; i < count; ++i)
{
memset(name, 0, sizeof(char) * 128);
glGetActiveAttrib(mHandle, (GLuint)i, 128, &length, &size, &type, name);
int attrib = glGetAttribLocation(mHandle, name);
if (attrib >= 0)
mAttributes[name] = attrib;
}
glUseProgram(0);
}
void Shader::PopulateUniforms()
{
int count = -1;
int length;
char name[128];
int size;
GLenum type;
char testName[256];
glUseProgram(mHandle);
glGetProgramiv(mHandle, GL_ACTIVE_UNIFORMS, &count);
for (int i = 0; i < count; ++i)
{
memset(name, 0, sizeof(char) * 128);
glGetActiveUniform(mHandle, (GLuint)i, 128, &length, &size, &type, name);
int uniform = glGetUniformLocation(mHandle, name);
if (uniform >= 0)
{
std::string uniformName = name;
std::size_t found = uniformName.find('[');
if (found != std::string::npos)
{
uniformName.erase(uniformName.begin() + found, uniformName.end());
// Populate subscripted names too
unsigned int uniformIndex = 0;
while (true)
{
memset(testName, 0, sizeof(char) * 256);
sprintf(testName, "%s[%d]", uniformName.c_str(), uniformIndex++);
int uniformLocation = glGetUniformLocation(mHandle, testName);
if (uniformLocation < 0)
break;
mUniforms[testName] = uniformLocation;
}
}
mUniforms[uniformName] = uniform;
}
}
glUseProgram(0);
}
// 这个Load函数, 参数既可以是vs和fg的shader的路径
// 也可以是直接代表shader内容的长string@
void Shader::Load(const std::string& vertex, const std::string& fragment)
{
std::ifstream f(vertex.c_str());
bool vertFile = f.good();
f.close();
f = std::ifstream(vertex.c_str());
bool fragFile = f.good();
f.close();
std::string v_source = vertex;
if (vertFile)
v_source = ReadFile(vertex);
std::string f_source = fragment;
if (fragFile)
f_source = ReadFile(fragment);
unsigned int v_shader = CompileVertexShader(v_source);
unsigned int f_shader = CompileFragmentShader(f_source);
if (LinkShaders(v_shader, f_shader))
{
PopulateAttributes();
PopulateUniforms();
}
}
void Shader::Bind()
{
glUseProgram(mHandle);
}
void Shader::UnBind()
{
glUseProgram(0);
}
unsigned int Shader::GetHandle()
{
return mHandle;
}
unsigned int Shader::GetAttribute(const std::string& name)
{
std::map<std::string, unsigned int>::iterator it = mAttributes.find(name);
if (it == mAttributes.end())
{
std::cout << "Retrieving bad attribute index: " << name << "\n";
return 0;
}
return it->second;
}
unsigned int Shader::GetUniform(const std::string& name)
{
std::map<std::string, unsigned int>::iterator it = mUniforms.find(name);
if (it == mUniforms.end())
{
std::cout << "Retrieving bad uniform index: " << name << "\n";
return 0;
}
return it->second;
}
Working with buffers (attributes)
A vertex is made up of attributes. For example, a vertex has a position and a normal, which are both attributes.
The Attribute class declaration
创建Attribute.h文件:
#ifndef _H_ATTRIBUTE_
#define _H_ATTRIBUTE_
#include <vector>
// 模板类, 可以存储任何顶点属性的数据
template<typename T>
class Attribute
{
protected:
unsigned int mHandle;
unsigned int mCount;
private:
// 同样是不允许Attribute对象复制, 因为它传给GPU就可以了
Attribute(const Attribute& other);
Attribute& operator=(const Attribute& other);
void SetAttribPointer(unsigned int slot);// 调用glVertexAttribIPointer
public:
Attribute();// 构造函数里调用glGenBuffers, 得到的handle赋给mHandle
~Attribute();
// Set函数Set的是GPU里的数据, 其实是Upload CPU数据到GPU
// 内部调用的是glBindBuffer和glBufferData
// Set函数接受两种形式的T类型的数组
void Set(T* inputArray, unsigned int arrayLength);
void Set(std::vector<T>& input);
// 底层应该是调用glVertexArrayAttrib
void BindTo(unsigned int slot);
void UnBindFrom(unsigned int slot);
unsigned int Count();// return mCount
unsigned int GetHandle();// return mHandle
};
#endif
Implementing the Attribute class
#include "Attribute.h"
#include "glad.h"
#include "vec2.h"
#include "vec3.h"
#include "vec4.h"
#include "quat.h"
template Attribute<int>;
template Attribute<float>;
template Attribute<vec2>;
template Attribute<vec3>;
template Attribute<vec4>;
template Attribute<ivec4>;
template Attribute<quat>;
template<typename T>
Attribute<T>::Attribute()
{
glGenBuffers(1, &mHandle);
mCount = 0;
}
template<typename T>
Attribute<T>::~Attribute()
{
glDeleteBuffers(1, &mHandle);
}
template<typename T>
unsigned int Attribute<T>::Count()
{
return mCount;
}
template<typename T>
unsigned int Attribute<T>::GetHandle()
{
return mHandle;
}
template<typename T>
void Attribute<T>::Set(T* inputArray, unsigned int arrayLength)
{
mCount = arrayLength;
unsigned int size = sizeof(T);
glBindBuffer(GL_ARRAY_BUFFER, mHandle);
glBufferData(GL_ARRAY_BUFFER, size * mCount, inputArray, GL_STREAM_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
template<typename T>
void Attribute<T>::Set(std::vector<T>& input)
{
Set(&input[0], (unsigned int)input.size());
}
// 这里直接利用模板特化, 写出了各种顶点数据类型调用的不同的glVertexAttribIPointer函数, 有:
// int, ivec4, float, vec2, vec3, vec4, quat
// int数组数据放到VAO的第slot号槽位
template<>
void Attribute<int>::SetAttribPointer(unsigned int slot)
{
glVertexAttribIPointer(slot, 1, GL_INT, 0, (void*)0);// 注意这里的IPointer
}
// ivec4数组数据放到VAO的第slot号槽位
template<>
void Attribute<ivec4>::SetAttribPointer(unsigned int slot)
{
glVertexAttribIPointer(slot, 4, GL_INT, 0, (void*)0);// 注意这里的IPointer
}
// float数组数据放到VAO的第slot号槽位
template<>
void Attribute<float>::SetAttribPointer(unsigned int slot)
{
glVertexAttribPointer(slot, 1, GL_FLOAT, GL_FALSE, 0, (void*)0);
}
// vec2数组数据放到VAO的第slot号槽位, 比如normal
template<>
void Attribute<vec2>::SetAttribPointer(unsigned int slot)
{
glVertexAttribPointer(slot, 2, GL_FLOAT, GL_FALSE, 0, (void*)0);
}
template<>
void Attribute<vec3>::SetAttribPointer(unsigned int slot)
{
glVertexAttribPointer(slot, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
}
template<>
void Attribute<vec4>::SetAttribPointer(unsigned int slot)
{
glVertexAttribPointer(slot, 4, GL_FLOAT, GL_FALSE, 0, (void*)0);
}
template<>
void Attribute<quat>::SetAttribPointer(unsigned int slot)
{
glVertexAttribPointer(slot, 4, GL_FLOAT, GL_FALSE, 0, (void*)0);
}
template<typename T>
void Attribute<T>::BindTo(unsigned int slot)
{
glBindBuffer(GL_ARRAY_BUFFER, mHandle);
glEnableVertexAttribArray(slot);
SetAttribPointer(slot);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
template<typename T>
void Attribute<T>::UnBindFrom(unsigned int slot)
{
glBindBuffer(GL_ARRAY_BUFFER, mHandle);
glDisableVertexAttribArray(slot);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
创建uniform类
前面的Attribute类是有实例化的对象的，代表每个顶点的数据，这里的Uniform类也是个模板类，但是没有实例化对象，只有public static函数，因为它里面的数据是所有顶点共享的。
对于每种uniform的数据类型T而言，需要设置三个函数：
- 设置单独的一个uniform，设置一个T的值
- 设置T对应的uniform的数组的值
- 与2作用相同，但是接受的是vector数组(for convenience)
Uniform.h如下:
#ifndef _H_UNIFORM_
#define _H_UNIFORM_
#include <vector>
template <typename T>
class Uniform
{
private:
// 私有构造函数, 防止类实例化(感觉是不是也可以用纯虚函数)
Uniform();
Uniform(const Uniform&);
Uniform& operator=(const Uniform&);
~Uniform();
public:
// 感觉用Upload的函数命名是不是比Set好一些
static void Set(unsigned int slot, const T& value);
static void Set(unsigned int slot, T* inputArray, unsigned int arrayLength);
static void Set(unsigned int slot, std::vector<T>& inputArray);
};
#endif
Uniform.cpp如下:
#include "Uniform.h"
#include "glad.h"
#include "vec2.h"
#include "vec3.h"
#include "vec4.h"
#include "quat.h"
#include "mat4.h"
// 由于这些Uniform的模板实现在宏里, 为了使用到的时候通过编译, 需要加这些东西
template Uniform<int>;
template Uniform<ivec4>;
template Uniform<ivec2>;
template Uniform<float>;
template Uniform<vec2>;
template Uniform<vec3>;
template Uniform<vec4>;
template Uniform<quat>;
template Uniform<mat4>;
// 为tType类型实现Uniform的模板偏特化
#define UNIFORM_IMPL(gl_func, tType, dType) \
template<> \
void Uniform<tType>::Set(unsigned int slot, tType* data, unsigned int length) { \
gl_func(slot, (GLsizei)length, (dType*)&data[0]); \
}
//第一个int是uniform对应的数据类型, 第二个int是uniform对应的数据在内存里的类型
UNIFORM_IMPL(glUniform1iv, int, int)
// 上面这个宏等同于:
// template<> // int类型数据的模板特化
// void Uniform<int>::Set(unsigned int slot, int* data, unsigned int length)
// {
// glUniform1iv(slot, (GLsizei)length, (int*)&data[0]);
// }
// ivec4由4个int组成, 内存上本质上是int数组
UNIFORM_IMPL(glUniform4iv, ivec4, int)
UNIFORM_IMPL(glUniform2iv, ivec2, int)
UNIFORM_IMPL(glUniform1fv, float, float)
UNIFORM_IMPL(glUniform2fv, vec2, float)
UNIFORM_IMPL(glUniform3fv, vec3, float)
UNIFORM_IMPL(glUniform4fv, vec4, float)
UNIFORM_IMPL(glUniform4fv, quat, float)
// 上面的uniform上传函数都是三个参数, 所以统一用宏, 但是这里的mat4由四个参数, 所以单独特化
template<>
void Uniform<mat4>::Set(unsigned int slot, mat4* inputArray, unsigned int arrayLength)
{
glUniformMatrix4fv(slot, (GLsizei)arrayLength, false, (float*)&inputArray[0]);
}
// 保留只有两个参数的模板, 此时都是上传的单个Uniform数据
template <typename T>
void Uniform<T>::Set(unsigned int slot, const T& value)
{
Set(slot, (T*)&value, 1);
}
// 支持上传vector<T>的数组数据
template <typename T>
void Uniform<T>::Set(unsigned int slot, std::vector<T>& value)
{
Set(slot, &value[0], (unsigned int)value.size());
}
没啥稀奇的，我记得之前看的OpenGL教程里是把这块内容放到了Shader类里，这本书的代码里把它单独拆出来放到了Uniform类里。
创建Index Buffer类
与Attribute类类似:
// 头文件
#ifndef _H_INDEXBUFFER_
#define _H_INDEXBUFFER_
#include <vector>
class IndexBuffer
{
public:
unsigned int mHandle;
unsigned int mCount;
private:
// 不允许Copy
IndexBuffer(const IndexBuffer& other);
IndexBuffer& operator=(const IndexBuffer& other);
public:
IndexBuffer();// glGenBuffers(1, &mHandle)
~IndexBuffer();// glDeleteBuffers(1, &mHandle)
// Set就是把IndexBuffer上传给GPU, 就是调用glBindBuffer和glBufferData
void Set(unsigned int* inputArray, unsigned int arrayLengt);
void Set(std::vector<unsigned int>& input);
unsigned int Count();
unsigned int GetHandle();
};
#endif
// cpp文件
#include "IndexBuffer.h"
#include "glad.h"
IndexBuffer::IndexBuffer()
{
glGenBuffers(1, &mHandle);
mCount = 0;
}
IndexBuffer::~IndexBuffer()
{
glDeleteBuffers(1, &mHandle);
}
unsigned int IndexBuffer::Count()
{
return mCount;
}
unsigned int IndexBuffer::GetHandle()
{
return mHandle;
}
void IndexBuffer::Set(unsigned int* inputArray, unsigned int arrayLengt)
{
mCount = arrayLengt;
unsigned int size = sizeof(unsigned int);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mHandle);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, size * mCount, inputArray, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
void IndexBuffer::Set(std::vector<unsigned int>& input)
{
Set(&input[0], (unsigned int)input.size());
}
Rendering geometry
作者划分的也太细了，居然还有个Draw类(感觉叫Renderer类不是更好么)，讲道理感觉封装的过于细致了，没必要，Draw类就是把OpenGL的四个Draw Call函数给封装了起来，就是这四个：
glDrawArrays: 直接按输入的Primitive类型绘制，不需要Index BufferglDrawElements: 按照输入的Primitive类型和Index Buffer绘制glDrawArraysInstancedglDrawElementsInstanced
代码如下：
// 头文件
#ifndef _H_DRAW_
#define _H_DRAW_
#include "IndexBuffer.h"
enum class DrawMode
{
Points,
LineStrip,
LineLoop,
Lines,
Triangles,
TriangleStrip,
TriangleFan
};
void Draw(IndexBuffer& inIndexBuffer, DrawMode mode);
void Draw(unsigned int vertexCount, DrawMode mode);
void DrawInstanced(IndexBuffer& inIndexBuffer, DrawMode mode, unsigned int instanceCount);
void DrawInstanced(unsigned int vertexCount, DrawMode mode, unsigned int numInstances);
#endif
// cpp文件
#include "Draw.h"
#include "glad.h"
#include <iostream>
static GLenum DrawModeToGLEnum(DrawMode input)
{
switch (input)
{
case DrawMode::Points:
return GL_POINTS;
case DrawMode::LineStrip:
return GL_LINE_STRIP;
case DrawMode::LineLoop:
return GL_LINE_LOOP;
case DrawMode::Lines:
return GL_LINES;
case DrawMode::Triangles:
return GL_TRIANGLES;
case DrawMode::TriangleStrip:
return GL_TRIANGLE_STRIP;
case DrawMode::TriangleFan:
return GL_TRIANGLE_FAN;
}
std::cout << "DrawModeToGLEnum unreachable code hit\n";
return 0;
}
void Draw(unsigned int vertexCount, DrawMode mode)
{
glDrawArrays(DrawModeToGLEnum(mode), 0, vertexCount);
}
void DrawInstanced(unsigned int vertexCount, DrawMode mode, unsigned int numInstances)
{
glDrawArraysInstanced(DrawModeToGLEnum(mode), 0, vertexCount, numInstances);
}
void Draw(IndexBuffer& inIndexBuffer, DrawMode mode)
{
unsigned int handle = inIndexBuffer.GetHandle();
unsigned int numIndices = inIndexBuffer.Count();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, handle);
glDrawElements(DrawModeToGLEnum(mode), numIndices, GL_UNSIGNED_INT, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
void DrawInstanced(IndexBuffer& inIndexBuffer, DrawMode mode, unsigned int instanceCount)
{
unsigned int handle = inIndexBuffer.GetHandle();
unsigned int numIndices = inIndexBuffer.Count();
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, handle);
glDrawElementsInstanced(DrawModeToGLEnum(mode), numIndices, GL_UNSIGNED_INT, 0, instanceCount);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
Working with textures
此书里面所有的漫反射光都不是计算出来的，而都是从贴图里读取出来的，这里的图片都是png格式的，用stb_image库来读取进来。stb是一个文件库的集合(Stb is a collection of single-file public domain libraries)，代码在https://github.com/nothings/stb.
把对应的stb_image.h头文件加入到自己的项目里，然后创建一个对应的cpp文件，加cpp文件应该是为了让它被编译，代码如下：
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
然后就可以创建自己的Texture类了：
// 头文件
#ifndef _H_TEXTURE_
#define _H_TEXTURE_
class Texture
{
protected:
unsigned int mWidth;
unsigned int mHeight;
unsigned int mChannels;
unsigned int mHandle;
private:
Texture(const Texture& other);
Texture& operator=(const Texture& other);
public:
Texture();// glGenTextures
Texture(const char* path);// glGenTextures and load image(call Load function)
~Texture();// glDeleteTextures(1, &mHandle);
void Load(const char* path);
// bind并把texture作为uniform传给GPU
void Set(unsigned int uniformIndex, unsigned int textureIndex);
// 绑定到GL_TEXTURE0的第0槽位
void UnSet(unsigned int textureIndex);
unsigned int GetHandle();
};
#endif
// cpp文件
#include "Texture.h"
#include "stb_image.h"
#include "glad.h"
Texture::Texture()
{
mWidth = 0;
mHeight = 0;
mChannels = 0;
glGenTextures(1, &mHandle);
}
Texture::Texture(const char* path)
{
glGenTextures(1, &mHandle);
Load(path);
}
Texture::~Texture()
{
glDeleteTextures(1, &mHandle);
}
// load, bind, set uv and channels
void Texture::Load(const char* path)
{
glBindTexture(GL_TEXTURE_2D, mHandle);
int width, height, channels;
// 4代表读取RGBA四个通道
unsigned char* data = stbi_load(path, &width, &height, &channels, 4);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
// The Texture class will always load textures using the same mipmap level and wrapping parameters.
// For the samples in this book, that should be enough.(为啥mipmap等级会是相同的?)
glGenerateMipmap(GL_TEXTURE_2D);
stbi_image_free(data);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glBindTexture(GL_TEXTURE_2D, 0);
mWidth = width;
mHeight = height;
mChannels = channels;
}
void Texture::Set(unsigned int uniformIndex, unsigned int textureIndex)
{
glActiveTexture(GL_TEXTURE0 + textureIndex);// 激活Texture槽位
glBindTexture(GL_TEXTURE_2D, mHandle);
glUniform1i(uniformIndex, textureIndex);
}
void Texture::UnSet(unsigned int textureIndex)
{
glActiveTexture(GL_TEXTURE0 + textureIndex);
glBindTexture(GL_TEXTURE_2D, 0);
glActiveTexture(GL_TEXTURE0);
}
unsigned int Texture::GetHandle()
{
return mHandle;
}
添加具体的shaders文件
前面已经写好了Shader类了，以前学的OpenGL里的Shader是一个很多东西的类，这本书里把里面的Uniform、Texture类的东西都剥离出去了，这里补充vs和fs两个shader文件，就行了
// static.vert文件
// This shader can be used to display static geometry or CPU skinned meshes
#version 330 core
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;
in vec3 position;
in vec3 normal;
in vec2 texCoord;
out vec3 norm;
out vec3 fragPos;
out vec2 uv;
void main()
{
// 注意, 这里的mvp是以uniform的形式存在的, 每个顶点的MVP是一样的
gl_Position = projection * view * model * vec4(position, 1.0);
fragPos = vec3(model * vec4(position, 1.0));
norm = vec3(model * vec4(normal, 0.0f));
uv = texCoord;
}
// lit.frag文件
// Some chapters will introduce new vertex shaders, but the fragment shader is always going to remain as this one.
#version 330 core
in vec3 norm;
in vec3 fragPos;
in vec2 uv;
uniform vec3 light;
uniform sampler2D tex0;
out vec4 FragColor;
void main()
{
vec4 diffuseColor = texture(tex0, uv);
vec3 n = normalize(norm);
vec3 l = normalize(light);
float diffuseIntensity = clamp(dot(n, l) + 0.1, 0, 1);
// 这里的输出颜色只跟贴图中得到的光照颜色, 以及法线与光线的夹角有关
// 没有环境光和高光
FragColor = diffuseColor * diffuseIntensity;
}
总结
这一章的内容本来没想单独写一篇文章的，但是代码量确实有点大。这篇文章里说到的，对渲染的抽象，在我看来，只是在头文件里没有用到任何OpenGL的API而已，说是abstraction layer实在是有点勉强… 总之，算是对OpenGL的复习和巩固吧
这一章的github仓库里额外提供了一个DebugDraw类，可以帮助debug简单的图元，下一章会开始学习glTF这个文件格式。
