【OpenGL】卡通着色（Cell Shading)——将纹理单元作为光线

 

原理就是一维渐变纹理，将漫反射系数作为纹理坐标(x,y)从一维纹理采样得到拥有漫反射因子的光线强度颜色（即颜色带上了漫反射的影响）

// Cell lighting Shader
// Vertex Shader
// Richard S. Wright Jr.
// OpenGL SuperBible
#version 130

// Incoming per vertex... position and normal
in vec4 vVertex;
in vec3 vNormal;

smooth out float textureCoordinate;

uniform vec3	vLightPosition;
uniform mat4	mvpMatrix;
uniform mat4	mvMatrix;
uniform mat3	normalMatrix;


void main(void) 
    { 
    // Get surface normal in eye coordinates
    vec3 vEyeNormal = normalMatrix * vNormal;

    // Get vertex position in eye coordinates
    vec4 vPosition4 = mvMatrix * vVertex;
    vec3 vPosition3 = vPosition4.xyz / vPosition4.w;

    // Get vector to light source
    vec3 vLightDir = normalize(vLightPosition - vPosition3);

    // Dot product gives us diffuse intensity
    textureCoordinate = max(0.0, dot(vEyeNormal, vLightDir));

    // Don't forget to transform the geometry!
    gl_Position = mvpMatrix * vVertex;
    }

// Cell lighting Shader
// Fragment Shader
// Richard S. Wright Jr.
// OpenGL SuperBible
#version 130

uniform sampler1D colorTable;
out vec4 vFragColor;

smooth in float textureCoordinate;


void main(void)
   { 
   vFragColor = texture(colorTable, textureCoordinate);
   }

// ToonShader.cpp
// OpenGL SuperBible
// Demonstrates a simple toon shader
// Program by Richard S. Wright Jr.
#pragma comment(lib, "gltools.lib")
#include <GLTools.h>	// OpenGL toolkit
#include <GLMatrixStack.h>
#include <GLFrame.h>
#include <GLFrustum.h>
#include <GLGeometryTransform.h>
#include <StopWatch.h>

#include <math.h>
#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif


GLFrame             viewFrame;
GLFrustum           viewFrustum;
GLTriangleBatch     torusBatch;
GLMatrixStack       modelViewMatrix;
GLMatrixStack       projectionMatrix;
GLGeometryTransform transformPipeline;
GLShaderManager     shaderManager;

GLuint	toonShader;	        // The dissolving light shader
GLint	locLight;			// The location of the Light in eye coordinates
GLint	locMVP;				// The location of the ModelViewProjection matrix uniform
GLint	locMV;				// The location of the ModelView matrix uniform
GLint	locNM;				// The location of the Normal matrix uniform
GLint   locColorTable;		// The location of the color table

GLuint	texture;



// This function does any needed initialization on the rendering
// context. 
void SetupRC(void)
{
	// Background
	glClearColor(0.025f, 0.25f, 0.25f, 1.0f);

	glEnable(GL_DEPTH_TEST);

	shaderManager.InitializeStockShaders();
	viewFrame.MoveForward(4.0f);

	// Make the torus
	gltMakeTorus(torusBatch, .80f, 0.25f, 52, 26);

	toonShader = gltLoadShaderPairWithAttributes("ToonShader.vp", "ToonShader.fp", 2, GLT_ATTRIBUTE_VERTEX, "vVertex",
		GLT_ATTRIBUTE_NORMAL, "vNormal");

	locLight = glGetUniformLocation(toonShader, "vLightPosition");
	locMVP = glGetUniformLocation(toonShader, "mvpMatrix");
	locMV = glGetUniformLocation(toonShader, "mvMatrix");
	locNM = glGetUniformLocation(toonShader, "normalMatrix");
	locColorTable = glGetUniformLocation(toonShader, "colorTable");

	glGenTextures(1, &texture);
	glBindTexture(GL_TEXTURE_1D, texture);
	GLubyte textureData[4][3] = { 32,  0, 0,
								  64,  0, 0,
								  128, 0, 0,
								  255, 0, 0 };

	glTexImage1D(GL_TEXTURE_1D, 0, GL_RGB, 4, 0, GL_RGB, GL_UNSIGNED_BYTE, textureData);
	glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
}

// Cleanup
void ShutdownRC(void)
{
	glDeleteTextures(1, &texture);
}


// Called to draw scene
void RenderScene(void)
{
	static CStopWatch rotTimer;

	// Clear the window and the depth buffer
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	modelViewMatrix.PushMatrix(viewFrame);
	modelViewMatrix.Rotate(rotTimer.GetElapsedSeconds() * 10.0f, 0.0f, 1.0f, 0.0f);

	GLfloat vEyeLight[] = { -100.0f, 100.0f, 100.0f };
	GLfloat vAmbientColor[] = { 0.1f, 0.1f, 0.1f, 1.0f };
	GLfloat vDiffuseColor[] = { 0.1f, 1.0f, 0.1f, 1.0f };
	GLfloat vSpecularColor[] = { 1.0f, 1.0f, 1.0f, 1.0f };

	glUseProgram(toonShader);
	glUniform3fv(locLight, 1, vEyeLight);
	glUniformMatrix4fv(locMVP, 1, GL_FALSE, transformPipeline.GetModelViewProjectionMatrix());
	glUniformMatrix4fv(locMV, 1, GL_FALSE, transformPipeline.GetModelViewMatrix());
	glUniformMatrix3fv(locNM, 1, GL_FALSE, transformPipeline.GetNormalMatrix());
	glUniform1i(locColorTable, 0);
	torusBatch.Draw();

	modelViewMatrix.PopMatrix();


	glutSwapBuffers();
	glutPostRedisplay();
}



void ChangeSize(int w, int h)
{
	// Prevent a divide by zero
	if (h == 0)
		h = 1;

	// Set Viewport to window dimensions
	glViewport(0, 0, w, h);

	viewFrustum.SetPerspective(35.0f, float(w) / float(h), 1.0f, 100.0f);

	projectionMatrix.LoadMatrix(viewFrustum.GetProjectionMatrix());
	transformPipeline.SetMatrixStacks(modelViewMatrix, projectionMatrix);
}

///
// Main entry point for GLUT based programs
int main(int argc, char* argv[])
{
	gltSetWorkingDirectory(argv[0]);

	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL);
	glutInitWindowSize(800, 600);
	glutCreateWindow("Cell (toon) shading");
	glutReshapeFunc(ChangeSize);
	glutDisplayFunc(RenderScene);

	GLenum err = glewInit();
	if (GLEW_OK != err) {
		fprintf(stderr, "GLEW Error: %s\n", glewGetErrorString(err));
		return 1;
	}

	SetupRC();
	glutMainLoop();
	ShutdownRC();
	return 0;
}