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;
}