OpenGL学习笔记 第三周：shader的使用

attribute vec4 position;
attribute vec4 color;
attribute vec2 texcoord;
attribute vec4 normal;

uniform mat4 ModelMatrix;
uniform mat4 ViewMatrix;
uniform mat4 ProjectionMatrix;
uniform mat4 IT_ModelMatrix; // 模型空间到世界空间的转置矩阵，等同于Unity中的UnityObjectToWorldNormal

varying vec4 V_Color;
varying vec2 V_Texcoord;
varying vec4 V_Normal;
varying vec4 V_WorldPos;

void main()
{

	V_Normal = IT_ModelMatrix*normal;
	V_Texcoord = texcoord;
	V_WorldPos = ModelMatrix*position;
	V_Color = color;
	gl_Position=ProjectionMatrix*ViewMatrix*ModelMatrix*position;
}

#ifdef GL_ES
precision mediump float; //opengl es中需要定义浮点精度，否则可能运行不了
#endif

uniform sampler2D U_Texture;

uniform vec4 U_LightPos;        // 光源位置，W=0时就是平行光

uniform vec4 U_LightAmbient;    // 光的环境光分量
uniform vec4 U_AmbientMaterial; // 物体材质对环境光的反射系数

uniform vec4 U_LightDiffuse;
uniform vec4 U_DiffuseMaterial;

uniform vec4 U_LightSpecular;
uniform vec4 U_SpecularMaterial;

uniform vec4 U_CameraPos;
uniform vec4 U_LightOpt;

varying vec4 V_Color;
varying vec2 V_Texcoord;
varying vec4 V_Normal;
varying vec4 V_WorldPos;

vec4 GetPointLight()
{
	float distance=0.0;
	float constantFactor=1.0;
	float linearFactor=0.0;
	float quadricFactor=0.0;
	vec4 ambientColor=vec4(1.0,1.0,1.0,1.0)*vec4(0.1,0.1,0.1,1.0);
	vec3 L=vec3(0.0,1.0,0.0)-V_WorldPos.xyz;
	distance=length(L);
	float attenuation=1.0/(constantFactor+linearFactor*distance+quadricFactor*quadricFactor*distance);
	L=normalize(L);
	vec3 n=normalize(V_Normal.xyz);
	float diffuseIntensity=max(0.0,dot(L,n));
	vec4 diffuseColor=vec4(1.0,1.0,1.0,1.0)*vec4(0.1,0.4,0.6,1.0)*diffuseIntensity*attenuation;
	return ambientColor+diffuseColor;
}

// 接受的是vertex shader中生成的三角面，然后计算三角面上的像素的值。
// GPU中并行计算，并行的是计算像素这个事情
void main()
{
	/*  unity shader的写法
	fixed4 frag(v2f i) : SV_Target {
	// Get ambient term
	fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;

	fixed3 worldNormal = normalize(i.worldNormal);
	fixed3 worldLightDir = normalize(_WorldSpaceLightPos0.xyz);

	// Compute diffuse term
	fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal, worldLightDir));

	// Get the reflect direction in world space
	fixed3 reflectDir = normalize(reflect(-worldLightDir, worldNormal));
	// Get the view direction in world space
	fixed3 viewDir = normalize(_WorldSpaceCameraPos.xyz - i.worldPos.xyz);
	// Compute specular term
	fixed3 specular = _LightColor0.rgb * _Specular.rgb * pow(saturate(dot(reflectDir, viewDir)), _Gloss);

	return fixed4(ambient + diffuse + specular, 1.0);
	}*/

	vec4 ambientColor = U_LightAmbient * U_AmbientMaterial;
	
	vec3 lightPos = U_LightPos.xyz;
	vec3 L = lightPos;
	// 这里直接对U_LightPos.xyz对了归一化
	L = normalize(L);

	vec3 n = normalize(V_Normal.xyz);

	float diffuseIntensity = max(0.0, dot(L,n));
	vec4 diffuseColor = U_LightDiffuse*U_DiffuseMaterial*diffuseIntensity;

	vec4 specularColor = vec4(0.0,0.0,0.0,0.0);
	if(diffuseIntensity!=0)
	{
		vec3 reflectDir = normalize(reflect(-L,n));
		vec3 viewDir = normalize(U_CameraPos.xyz - V_WorldPos.xyz);
		specularColor = U_LightSpecular*U_SpecularMaterial*pow(max(0.0, dot(viewDir, reflectDir)), U_LightOpt.x);
	}
	if(U_LightOpt.y==1.0){
		gl_FragColor=(ambientColor+diffuseColor)*texture2D(U_Texture,V_Texcoord.xy)+specularColor;
	}else if(U_LightOpt.z==1.0){
		gl_FragColor=(ambientColor+diffuseColor+GetPointLight())*texture2D(U_Texture,V_Texcoord.xy);
	}else if(U_LightOpt.w==1.0){
		gl_FragColor=ambientColor+diffuseColor+specularColor;
	}
}

   glGenBuffers(1, &vbo); // 显存中申请一块内容，地址为vbo
float data[] = {
	-0.2f, -0.2f, -0.6f, 1.0f, /* color: */ 1.0f, 1.0f, 1.0f, 1.0f, /* texcoord: */ 0.0f, 0.0f,
	0.2f, -0.2f, -0.6f, 1.0f,  /* color: */ 0.0f, 1.0f, 0.0f, 1.0f, /* texcoord: */ 1.0f, 0.0f,
	0.0f, 0.2f, -0.6f, 1.0f,   /* color: */ 1.0f, 0.0f, 0.0f, 1.0f, /* texcoord: */ 0.5f, 1.0f
};

// 操作当前的vbo，类比glBindTexture
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// GL_STATIC_DRAW指的是放到GPU后不再动的数据
// 函数完成后数据从内存赋值到了显存，此时这个数据已经可以删除了
glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 30, data, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);

   GLuint vbo;
   GLuint program;
   GLint positionLocation;
   GLint modelMatrixLocation;
   GLint viewMatrixLocation;
   GLint projectionMatrixLocation;
   GLint colorLocation;
   GLint texcoordLocation;
   GLint textureLocation;
   glm::mat4 modelMatrix, viewMatrix, projectionMatrix;
   GLuint texture;
   
   ...
   
   // 位置不是按照shader代码里写的变量的顺序确定的
   positionLocation = glGetAttribLocation(program, "position");
colorLocation = glGetAttribLocation(program, "color");
texcoordLocation = glGetAttribLocation(program, "texcoord");

modelMatrixLocation = glGetUniformLocation(program, "ModelMatrix");
viewMatrixLocation = glGetUniformLocation(program, "ViewMatrix");
projectionMatrixLocation = glGetUniformLocation(program, "ProjectionMatrix");
textureLocation = glGetUniformLocation(program, "U_Texture");

... 

glUseProgram(program);
// 参数含义：插槽位置，几个矩阵（单插槽可以多矩阵），CPU传到GPU时是否需要转置，矩阵地址(从定义看是第一个数据的位置)
glUniformMatrix4fv(modelMatrixLocation, 1, GL_FALSE, glm::value_ptr(modelMatrix));
glUniformMatrix4fv(viewMatrixLocation, 1, GL_FALSE, glm::value_ptr(viewMatrix));
glUniformMatrix4fv(projectionMatrixLocation, 1, GL_FALSE, glm::value_ptr(projectionMatrix));

// 使用纹理
glBindTexture(GL_TEXTURE_2D, texture);
glUniform1i(textureLocation, 0);

glBindBuffer(GL_ARRAY_BUFFER, vbo);
// attribute插槽中某一个位置生效
glEnableVertexAttribArray(positionLocation);

// GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const void* pointer
// 插槽位置 ， 插槽中数据有几个分量（现在的位置是4个，xyzw），分量类型，
// 是否归一化（传入的如果不是float会变成float，e.g. 255,255,255,255→ 1.0,1.0,1.0,1.0)
// 紧挨着的两个点起始地址相距多远，这个位置信息从vbo的什么地址开始取值（从0号位置开始取值）
glVertexAttribPointer(positionLocation, 4, GL_FLOAT, GL_FALSE, sizeof(float) * 10, 0);

// 给color变量赋值
glEnableVertexAttribArray(colorLocation);
glVertexAttribPointer(colorLocation, 4, GL_FLOAT, GL_FALSE, sizeof(float) * 10, (void*)(sizeof(float) * 4));

// 给texcoord赋值
glEnableVertexAttribArray(texcoordLocation);
glVertexAttribPointer(texcoordLocation, 2, GL_FLOAT, GL_FALSE, sizeof(float) * 10, (void*)(sizeof(float) * 8));

// 绘制什么，从第几个点开始绘制，绘制几个三角形。
glDrawArrays(GL_TRIANGLES, 0, 3);

glBindBuffer(GL_ARRAY_BUFFER, 0);

glBindTexture(GL_TEXTURE_2D, 0);

glUseProgram(0);

struct a2v {
	float4 vertex : POSITION;
	float3 normal : NORMAL;
	float4 tangent : TANGENT;
	float4 texcoord : TEXCOORD0;
};