opengl 学习 之 11 lesson

opengl 学习 之 11 lesson

简介

2D纹理。简单来说就是用一个四边形的小框框，UV映射图片。

这里用了多个shader，一个是关于模型的，一个是关于图片的。

link

http://www.opengl-tutorial.org/uncategorized/2017/06/07/website-update/

步骤

bind the buffers, fifill them, select the shader program, bind the texture, enable/bind/confifigure the vertex attributes, enable the blending, and call glDrawArrays.

code

// Include standard headers
#include <stdio.h>
#include <stdlib.h>
#include <vector>

// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <GLFW/glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
using namespace glm;

#include <common/shader.hpp>
#include <common/texture.hpp>
#include <common/controls.hpp>
#include <common/objloader.hpp>
#include <common/vboindexer.hpp>
#include <common/text2D.hpp>

int main( void )
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		getchar();
		return -1;
	}

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Tutorial 11 - 2D Fonts", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		getchar();
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if (glewInit() != GLEW_OK) {
		fprintf(stderr, "Failed to initialize GLEW\n");
		getchar();
		glfwTerminate();
		return -1;
	}

	// Ensure we can capture the escape key being pressed below
	glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);
    // Hide the mouse and enable unlimited mouvement
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // Set the mouse at the center of the screen
    glfwPollEvents();
    glfwSetCursorPos(window, 1024/2, 768/2);

	// Dark blue background
	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

	// Enable depth test
	glEnable(GL_DEPTH_TEST);
	// Accept fragment if it closer to the camera than the former one
	glDepthFunc(GL_LESS); 

	// Cull triangles which normal is not towards the camera
	glEnable(GL_CULL_FACE);

	GLuint VertexArrayID;
	glGenVertexArrays(1, &VertexArrayID);
	glBindVertexArray(VertexArrayID);

	// Create and compile our GLSL program from the shaders
	GLuint programID = LoadShaders( "StandardShading.vertexshader", "StandardShading.fragmentshader" );

	// Get a handle for our "MVP" uniform
	GLuint MatrixID = glGetUniformLocation(programID, "MVP");
	GLuint ViewMatrixID = glGetUniformLocation(programID, "V");
	GLuint ModelMatrixID = glGetUniformLocation(programID, "M");

	// Load the texture
	GLuint Texture = loadDDS("uvmap.DDS");

	// Get a handle for our "myTextureSampler" uniform
	GLuint TextureID = glGetUniformLocation(programID, "myTextureSampler");

	// Read our .obj file
	std::vector<glm::vec3> vertices;
	std::vector<glm::vec2> uvs;
	std::vector<glm::vec3> normals;
	bool res = loadOBJ("suzanne.obj", vertices, uvs, normals);

	std::vector<unsigned short> indices;
	std::vector<glm::vec3> indexed_vertices;
	std::vector<glm::vec2> indexed_uvs;
	std::vector<glm::vec3> indexed_normals;
	indexVBO(vertices, uvs, normals, indices, indexed_vertices, indexed_uvs, indexed_normals);

	// Load it into a VBO

	GLuint vertexbuffer;
	glGenBuffers(1, &vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_vertices.size() * sizeof(glm::vec3), &indexed_vertices[0], GL_STATIC_DRAW);

	GLuint uvbuffer;
	glGenBuffers(1, &uvbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_uvs.size() * sizeof(glm::vec2), &indexed_uvs[0], GL_STATIC_DRAW);

	GLuint normalbuffer;
	glGenBuffers(1, &normalbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
	glBufferData(GL_ARRAY_BUFFER, indexed_normals.size() * sizeof(glm::vec3), &indexed_normals[0], GL_STATIC_DRAW);

	// Generate a buffer for the indices as well
	GLuint elementbuffer;
	glGenBuffers(1, &elementbuffer);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned short), &indices[0], GL_STATIC_DRAW);

	// Get a handle for our "LightPosition" uniform
	glUseProgram(programID);
	GLuint LightID = glGetUniformLocation(programID, "LightPosition_worldspace");

	// Initialize our little text library with the Holstein font
	initText2D( "Holstein.DDS" );

	// For speed computation
	double lastTime = glfwGetTime();
	int nbFrames = 0;

	do{

		// Measure speed
		double currentTime = glfwGetTime();
		nbFrames++;
		if ( currentTime - lastTime >= 1.0 ){ // If last prinf() was more than 1sec ago
			// printf and reset
			printf("%f ms/frame\n", 1000.0/double(nbFrames));
			nbFrames = 0;
			lastTime += 1.0;
		}

		// Clear the screen
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(programID);

		// Compute the MVP matrix from keyboard and mouse input
		computeMatricesFromInputs();
		glm::mat4 ProjectionMatrix = getProjectionMatrix();
		glm::mat4 ViewMatrix = getViewMatrix();
		glm::mat4 ModelMatrix = glm::mat4(1.0);
		glm::mat4 MVP = ProjectionMatrix * ViewMatrix * ModelMatrix;

		// Send our transformation to the currently bound shader,
		// in the "MVP" uniform
		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);
		glUniformMatrix4fv(ModelMatrixID, 1, GL_FALSE, &ModelMatrix[0][0]);
		glUniformMatrix4fv(ViewMatrixID, 1, GL_FALSE, &ViewMatrix[0][0]);

		glm::vec3 lightPos = glm::vec3(4,4,4);
		glUniform3f(LightID, lightPos.x, lightPos.y, lightPos.z);

		// Bind our texture in Texture Unit 0
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, Texture);
		// Set our "myTextureSampler" sampler to use Texture Unit 0
		glUniform1i(TextureID, 0);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		// 2nd attribute buffer : UVs
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
		glVertexAttribPointer(
			1,                                // attribute
			2,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// 3rd attribute buffer : normals
		glEnableVertexAttribArray(2);
		glBindBuffer(GL_ARRAY_BUFFER, normalbuffer);
		glVertexAttribPointer(
			2,                                // attribute
			3,                                // size
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// Index buffer
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementbuffer);

		// Draw the triangles !
		glDrawElements(
			GL_TRIANGLES,      // mode
			indices.size(),    // count
			GL_UNSIGNED_SHORT, // type
			(void*)0           // element array buffer offset
		);

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);
		glDisableVertexAttribArray(2);

		char text[256];
		sprintf(text,"%.2f sec", glfwGetTime() );
		printText2D(text, 10, 500, 60);

		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();

	} // Check if the ESC key was pressed or the window was closed
	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
		   glfwWindowShouldClose(window) == 0 );

	// Cleanup VBO, shader and texture
	glDeleteBuffers(1, &vertexbuffer);
	glDeleteBuffers(1, &uvbuffer);
	glDeleteBuffers(1, &normalbuffer);
	glDeleteBuffers(1, &elementbuffer);
	glDeleteProgram(programID);
	glDeleteTextures(1, &Texture);
	glDeleteVertexArrays(1, &VertexArrayID);

	// Delete the text's VBO, the shader and the texture
	cleanupText2D();

	// Close OpenGL window and terminate GLFW
	glfwTerminate();

	return 0;
}

#ifndef TEXT2D_HPP
#define TEXT2D_HPP

void initText2D(const char * texturePath);
void printText2D(const char * text, int x, int y, int size);
void cleanupText2D();

#endif

#include <vector>
#include <cstring>

#include <GL/glew.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
using namespace glm;

#include "shader.hpp"
#include "texture.hpp"

#include "text2D.hpp"

unsigned int Text2DTextureID;
unsigned int Text2DVertexBufferID;
unsigned int Text2DUVBufferID;
unsigned int Text2DShaderID;
unsigned int Text2DUniformID;

void initText2D(const char * texturePath){

	// Initialize texture
	Text2DTextureID = loadDDS(texturePath);

	// Initialize VBO
	glGenBuffers(1, &Text2DVertexBufferID);
	glGenBuffers(1, &Text2DUVBufferID);

	// Initialize Shader
	Text2DShaderID = LoadShaders( "TextVertexShader.vertexshader", "TextVertexShader.fragmentshader" );

	// Initialize uniforms' IDs
	Text2DUniformID = glGetUniformLocation( Text2DShaderID, "myTextureSampler" );

}

void printText2D(const char * text, int x, int y, int size){

	unsigned int length = strlen(text);

	// Fill buffers
	std::vector<glm::vec2> vertices;
	std::vector<glm::vec2> UVs;
	for ( unsigned int i=0 ; i<length ; i++ ){

		glm::vec2 vertex_up_left    = glm::vec2( x+i*size     , y+size );
		glm::vec2 vertex_up_right   = glm::vec2( x+i*size+size, y+size );
		glm::vec2 vertex_down_right = glm::vec2( x+i*size+size, y      );
		glm::vec2 vertex_down_left  = glm::vec2( x+i*size     , y      );

		vertices.push_back(vertex_up_left   );
		vertices.push_back(vertex_down_left );
		vertices.push_back(vertex_up_right  );

		vertices.push_back(vertex_down_right);
		vertices.push_back(vertex_up_right);
		vertices.push_back(vertex_down_left);

		char character = text[i];
		float uv_x = (character%16)/16.0f;
		float uv_y = (character/16)/16.0f;

		glm::vec2 uv_up_left    = glm::vec2( uv_x           , uv_y );
		glm::vec2 uv_up_right   = glm::vec2( uv_x+1.0f/16.0f, uv_y );
		glm::vec2 uv_down_right = glm::vec2( uv_x+1.0f/16.0f, (uv_y + 1.0f/16.0f) );
		glm::vec2 uv_down_left  = glm::vec2( uv_x           , (uv_y + 1.0f/16.0f) );
		UVs.push_back(uv_up_left   );
		UVs.push_back(uv_down_left );
		UVs.push_back(uv_up_right  );

		UVs.push_back(uv_down_right);
		UVs.push_back(uv_up_right);
		UVs.push_back(uv_down_left);
	}
	glBindBuffer(GL_ARRAY_BUFFER, Text2DVertexBufferID);
	glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(glm::vec2), &vertices[0], GL_STATIC_DRAW);
	glBindBuffer(GL_ARRAY_BUFFER, Text2DUVBufferID);
	glBufferData(GL_ARRAY_BUFFER, UVs.size() * sizeof(glm::vec2), &UVs[0], GL_STATIC_DRAW);

	// Bind shader
	glUseProgram(Text2DShaderID);

	// Bind texture
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, Text2DTextureID);
	// Set our "myTextureSampler" sampler to use Texture Unit 0
	glUniform1i(Text2DUniformID, 0);

	// 1rst attribute buffer : vertices
	glEnableVertexAttribArray(0);
	glBindBuffer(GL_ARRAY_BUFFER, Text2DVertexBufferID);
	glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, (void*)0 );

	// 2nd attribute buffer : UVs
	glEnableVertexAttribArray(1);
	glBindBuffer(GL_ARRAY_BUFFER, Text2DUVBufferID);
	glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (void*)0 );

	glEnable(GL_BLEND);
	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	// Draw call
	glDrawArrays(GL_TRIANGLES, 0, vertices.size() );

	glDisable(GL_BLEND);

	glDisableVertexAttribArray(0);
	glDisableVertexAttribArray(1);

}

void cleanupText2D(){

	// Delete buffers
	glDeleteBuffers(1, &Text2DVertexBufferID);
	glDeleteBuffers(1, &Text2DUVBufferID);

	// Delete texture
	glDeleteTextures(1, &Text2DTextureID);

	// Delete shader
	glDeleteProgram(Text2DShaderID);
}

#version 330 core

// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec2 vertexPosition_screenspace;
layout(location = 1) in vec2 vertexUV;

// Output data ; will be interpolated for each fragment.
out vec2 UV;

void main(){

	// Output position of the vertex, in clip space
	// map [0..800][0..600] to [-1..1][-1..1]
	vec2 vertexPosition_homoneneousspace = vertexPosition_screenspace - vec2(400,300); // [0..800][0..600] -> [-400..400][-300..300]
	vertexPosition_homoneneousspace /= vec2(400,300);
	gl_Position =  vec4(vertexPosition_homoneneousspace,0,1);

	// UV of the vertex. No special space for this one.
	UV = vertexUV;
}

#version 330 core

// Interpolated values from the vertex shaders
in vec2 UV;

// Ouput data
out vec4 color;

// Values that stay constant for the whole mesh.
uniform sampler2D myTextureSampler;

void main(){

	color = texture( myTextureSampler, UV );

}