OpenGL 入门教程(三) -- 混合

// Blending.cpp
// Move a Block based on arrow key movements,
// Blend it with background blocks

#include <GLTools.h>	// OpenGL toolkit
#include <GLShaderManager.h>

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

GLBatch	squareBatch;
GLBatch greenBatch;
GLBatch redBatch;
GLBatch blueBatch;
GLBatch blackBatch;

GLShaderManager	shaderManager;

GLfloat blockSize = 0.2f;
GLfloat vVerts[] = { -blockSize, -blockSize, 0.0f,
blockSize, -blockSize, 0.0f,
blockSize, blockSize, 0.0f,
-blockSize, blockSize, 0.0f };

///////////////////////////////////////////////////////////////////////////////
// This function does any needed initialization on the rendering context.
// This is the first opportunity to do any OpenGL related tasks.
void SetupRC()
{
// Black background
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);

shaderManager.InitializeStockShaders();

// Load up a triangle fan
squareBatch.Begin(GL_TRIANGLE_FAN, 4);
squareBatch.CopyVertexData3f(vVerts);
squareBatch.End();

GLfloat vBlock[] = { 0.25f, 0.25f, 0.0f,
0.75f, 0.25f, 0.0f,
0.75f, 0.75f, 0.0f,
0.25f, 0.75f, 0.0f };

greenBatch.Begin(GL_TRIANGLE_FAN, 4);
greenBatch.CopyVertexData3f(vBlock);
greenBatch.End();

GLfloat vBlock2[] = { -0.75f, 0.25f, 0.0f,
-0.25f, 0.25f, 0.0f,
-0.25f, 0.75f, 0.0f,
-0.75f, 0.75f, 0.0f };

redBatch.Begin(GL_TRIANGLE_FAN, 4);
redBatch.CopyVertexData3f(vBlock2);
redBatch.End();

GLfloat vBlock3[] = { -0.75f, -0.75f, 0.0f,
-0.25f, -0.75f, 0.0f,
-0.25f, -0.25f, 0.0f,
-0.75f, -0.25f, 0.0f };

blueBatch.Begin(GL_TRIANGLE_FAN, 4);
blueBatch.CopyVertexData3f(vBlock3);
blueBatch.End();

GLfloat vBlock4[] = { 0.25f, -0.75f, 0.0f,
0.75f, -0.75f, 0.0f,
0.75f, -0.25f, 0.0f,
0.25f, -0.25f, 0.0f };

blackBatch.Begin(GL_TRIANGLE_FAN, 4);
blackBatch.CopyVertexData3f(vBlock4);
blackBatch.End();
}

// Respond to arrow keys by moving the camera frame of reference
void SpecialKeys(int key, int x, int y)
{
GLfloat stepSize = 0.025f;

GLfloat blockX = vVerts[0];   // Upper left X
GLfloat blockY = vVerts[7];  // Upper left Y

if (key == GLUT_KEY_UP)
blockY += stepSize;

if (key == GLUT_KEY_DOWN)
blockY -= stepSize;

if (key == GLUT_KEY_LEFT)
blockX -= stepSize;

if (key == GLUT_KEY_RIGHT)
blockX += stepSize;

// Collision detection
if (blockX < -1.0f) blockX = -1.0f;
if (blockX > (1.0f - blockSize * 2)) blockX = 1.0f - blockSize * 2;;
if (blockY < -1.0f + blockSize * 2)  blockY = -1.0f + blockSize * 2;
if (blockY > 1.0f) blockY = 1.0f;

// Recalculate vertex positions
vVerts[0] = blockX;
vVerts[1] = blockY - blockSize * 2;

vVerts[3] = blockX + blockSize * 2;
vVerts[4] = blockY - blockSize * 2;

vVerts[6] = blockX + blockSize * 2;
vVerts[7] = blockY;

vVerts[9] = blockX;
vVerts[10] = blockY;

squareBatch.CopyVertexData3f(vVerts);

glutPostRedisplay();
}

///////////////////////////////////////////////////////////////////////////////
// Called to draw scene
void RenderScene(void)
{
// Clear the window with current clearing color
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

GLfloat vRed[] = { 1.0f, 0.0f, 0.0f, 0.5f };
GLfloat vGreen[] = { 0.0f, 1.0f, 0.0f, 1.0f };
GLfloat vBlue[] = { 0.0f, 0.0f, 1.0f, 1.0f };
GLfloat vBlack[] = { 0.0f, 0.0f, 0.0f, 1.0f };

shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vGreen);
greenBatch.Draw();

shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);
redBatch.Draw();

shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlue);
blueBatch.Draw();

shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vBlack);
blackBatch.Draw();

glEnable(GL_BLEND);//启动混合
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);//混合函数
shaderManager.UseStockShader(GLT_SHADER_IDENTITY, vRed);//设置当前存储着色器为填充模式
squareBatch.Draw();
glDisable(GL_BLEND);

// Flush drawing commands
glutSwapBuffers();
}

///////////////////////////////////////////////////////////////////////////////
// Window has changed size, or has just been created. In either case, we need
// to use the window dimensions to set the viewport and the projection matrix.
void ChangeSize(int w, int h)
{
glViewport(0, 0, w, h);
}

///////////////////////////////////////////////////////////////////////////////
// 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);
glutInitWindowSize(800, 600);
glutCreateWindow("Move Block with Arrow Keys to see blending");

GLenum err = glewInit();
if (GLEW_OK != err)
{
// Problem: glewInit failed, something is seriously wrong.
fprintf(stderr, "Error: %s\n", glewGetErrorString(err));
return 1;
}

glutReshapeFunc(ChangeSize);
glutDisplayFunc(RenderScene);
glutSpecialFunc(SpecialKeys);

SetupRC();

glutMainLoop();
return 0;
}