#include "utils.h"

/**
* 编译一个shader
*/
GLuint CompileShader(GLenum shaderType, const char * shaderCode)
{
	GLuint shader = glCreateShader(shaderType);//根据给定的shader类型创建shader
	glShaderSource(shader, 1, &shaderCode, nullptr);//1表示shader只有一行代码
	glCompileShader(shader);//编译shader

	//判断shader是的编译成功
	GLint compileResult = GL_TRUE;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &compileResult);
	if (compileResult == GL_FALSE) {
		char szLog[1024] = { 0 };
		GLsizei logLen = 0;
		glGetShaderInfoLog(shader, 1024, &logLen, szLog);
		printf("Compile Shader fail error log : %s \nshader code :\n%s\n", szLog, shaderCode);
		glDeleteShader(shader);
		shader = 0;
	}
	return shader;
}
/**
* 把编译好的vsShader和fsShader链接创建成一个shader程序
*/
GLuint CreateProgram(GLuint vsShader, GLuint fsShader)
{
	GLuint program = glCreateProgram();//先创建一个shader程序
	glAttachShader(program, vsShader);//绑定编译好的shader
	glAttachShader(program, fsShader);
	glLinkProgram(program);//链接成一个程序
	glDetachShader(program, vsShader);
	glDetachShader(program, fsShader);
	GLint nResult;
	glGetProgramiv(program, GL_LINK_STATUS, &nResult);
	if (nResult == GL_FALSE) {
		char log[1024] = { 0 };
		GLsizei writed = 0;
		glGetProgramInfoLog(program, 1024, &writed, log);
		printf("create gpu program fail,link error : %s\n", log);
		glDeleteProgram(program);
		program = 0;
	}
	return program;
}
unsigned char* DecodeBMP(unsigned char*bmpFileData, int&width, int&height) {
	if (0x4D42 == *((unsigned short*)bmpFileData)) {
		int pixelDataOffset = *((int*)(bmpFileData + 10));
		width = *((int*)(bmpFileData + 18));
		height = *((int*)(bmpFileData + 22));
		unsigned char*pixelData = bmpFileData + pixelDataOffset;
		for (int i = 0; i < width*height * 3; i += 3) {
			unsigned char temp = pixelData[i];
			pixelData[i] = pixelData[i + 2];
			pixelData[i + 2] = temp;
		}
		return pixelData;
	}
	return nullptr;
}
GLuint CreateTexture2D(unsigned char*pixelData, int width, int height, GLenum type) {
	GLuint texture;
	glGenTextures(1, &texture);
	glBindTexture(GL_TEXTURE_2D, texture);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
	glTexImage2D(GL_TEXTURE_2D, 0, type, width, height, 0, type, GL_UNSIGNED_BYTE, pixelData);
	glBindTexture(GL_TEXTURE_2D, 0);
	return texture;
}
GLuint CreateTexture2DFromBMP(const char*bmpPath) {
	int nFileSize = 0;
	unsigned char *bmpFileContent = LoadFileContent(bmpPath, nFileSize);
	if (bmpFileContent == nullptr) {
		return 0;
	}
	int bmpWidth = 0, bmpHeight = 0;
	unsigned char*pixelData = DecodeBMP(bmpFileContent, bmpWidth, bmpHeight);
	if (bmpWidth == 0) {
		delete bmpFileContent;
		return 0;
	}
	GLuint texture = CreateTexture2D(pixelData, bmpWidth, bmpHeight, GL_RGB);
	delete bmpFileContent;
	return texture;
}
GLuint CreateBufferObject(GLenum bufferType, GLsizeiptr size, GLenum usage, void*data /* = nullptr */) {
	GLuint object;
	glGenBuffers(1, &object);
	glBindBuffer(bufferType, object);
	glBufferData(bufferType, size, data, usage);
	glBindBuffer(bufferType, 0);
	return object;
}

GLuint CreateProcedureTexture(int size)
{
	unsigned char *imageData = new unsigned char[size*size * 4];
	float halfSize = (float)size / 2.0f;
	float maxDistance = sqrtf(halfSize*halfSize + halfSize*halfSize);
	float centerX = halfSize;
	float centerY = halfSize;
	for (int y = 0; y < size; ++y) {
		for (int x = 0; x < size; ++x) {
			int currentPixelOffset = (x + y*size) * 4;
			imageData[currentPixelOffset] = 255;
			imageData[currentPixelOffset + 1] = 255;
			imageData[currentPixelOffset + 2] = 255;
			float deltaX = (float)x - centerX;
			float deltaY = (float)y - centerY;
			float distance = sqrtf(deltaX*deltaX + deltaY*deltaY);
			float alpha = powf(1.0f - (distance / maxDistance), 8.0f);
			alpha = alpha > 1.0f ? 1.0f : alpha;
			imageData[currentPixelOffset + 3] = (unsigned char)(alpha*255.0f);
		}
	}
	GLuint texture = CreateTexture2D(imageData, size, size, GL_RGBA);
	delete imageData;
	return texture;
}