QT中学习Opengl---（纹理环绕方式与过滤）

前言：

本文的代码是 LearnOpenGL 中对应代码，这里提供学习，大家喜欢的可去官方网站去看看:

LearnOpenGL-CNhttps://learnopengl-cn.readthedocs.io/zh/latest/本章简单使用不同的环绕方式，来显示不同的纹理方案。

Texture Wrapping

纹理坐标通常的范围是从(0, 0)到(1, 1)，如果我们把纹理坐标设置为范围以外会发生什么？
OpenGL默认的行为是重复这个纹理图像(我们简单地忽略浮点纹理坐标的整数部分)，但
OpenGL提供了更多的选择：

环绕方式	描述
GL_REPEAT	纹理的默认行为，重复纹理图像
GL_MIRRORED_REPEAT	和 GL_REPEAT 一样，除了重复的图片是镜像放置的
GL_CLAMP_TO_EDGE	纹理坐标会在0到1之间，超出的部分会重复纹理坐标的边缘，就是边缘被拉伸
GL_CLAMP_TO_BORDER	超出的部分是用户指定的边缘的颜色

对应的图标状况：

前面提到的选项都可以使用 glTexParameter 函数单独设置每个坐标轴 s 、 t (如果是使用3D
纹理那么还有一个 r )它们和 x 、 y ( z )是相等的。

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_MIRRORED_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_MIRRORED_REPEAT);

如果我们选择 GL_CLAMP_TO_BORDER 选项，我们还要指定一个边缘的颜色。这次使
用 glTexParameter 函数的 fv 后缀形式，加上 GL_TEXTURE_BORDER_COLOR 作为选项，这个函数需要我们传递一个边缘颜色的float数组作为颜色值：

float borderColor[] = { 1.0f, 1.0f, 0.0f, 1.0f };
glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);

例子：

顶点坐标：

float vertices[] = {// positions          // colors           // texture coords0.8f,  0.8f, 0.0f,   1.0f, 0.0f, 0.0f,   2.0f, 2.0f, // top right0.8f, -0.8f, 0.0f,   0.0f, 1.0f, 0.0f,   2.0f, 0.0f, // bottom right-0.8f, -0.8f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // bottom left-0.8f,  0.8f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 2.0f  // top left};unsigned int indices[] = {  // note that we start from 0!0, 1, 3,  // first Triangle1, 2, 3   // second Triangle
};

这里纹理我们不在是1 1，写出纹理超出部分。

顶点着色器写法：

#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec3 aColor;
layout (location = 2) in vec2 aTexCoord;out vec3 ourColor;
out vec2 TexCoord;void main()
{gl_Position = vec4(aPos, 1.0);ourColor = aColor;TexCoord = vec2(aTexCoord.x, aTexCoord.y);
}

片段着色器

#version 330 core
out vec4 FragColor;in vec3 ourColor;
in vec2 TexCoord;// texture samplers
uniform sampler2D texture1;
uniform sampler2D texture2;void main()
{// linearly interpolate between both textures (80% container, 20% awesomeface)//FragColor = mix(texture(texture1, TexCoord), texture(texture2, TexCoord), 0.2);FragColor =texture(texture2,TexCoord);
}

这里我们使用了纹理2

GL_CLAMP_TO_BORDER：

float borderColor[] = { 1.0f, 1.0f, 0.0f, 1.0f };
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);  // we want to repeat the awesomeface pattern so we kept it at GL_REPEAT
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);
glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);

效果：

我们可以看到，超出部分都用黄色代替了。

GL_CLAMP_TO_EDGE

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); // we want to repeat the awesomeface pattern so we kept it at GL_REPEAT
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

GL_MIRRORED_REPEAT：

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_MIRRORED_REPEAT);    // we want to repeat the awesomeface pattern so we kept it at GL_REPEATglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_MIRRORED_REPEAT);

效果：

GL_REPEAT：

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_REPEAT); // we want to repeat the awesomeface pattern so we kept it at GL_REPEATglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_REPEAT);

所有代码：

#ifndef BKQOPENGLW_H
#define BKQOPENGLW_H#include <QOpenGLWidget>
#include <QOpenGLFunctions_3_3_Core>
#include <QOpenGLShaderProgram>
#include <QOpenGLTexture>
class BKQOpenglW : public QOpenGLWidget, QOpenGLFunctions_3_3_Core
{Q_OBJECT
public:enum Shape{None,Rect,circle,Triangle};explicit BKQOpenglW(QWidget *parent = nullptr);~BKQOpenglW();void drawShapes(Shape shape);void setWireFrame(bool b);
protected:virtual void initializeGL();virtual void resizeGL(int w, int h);virtual void paintGL();signals:public slots:private:
unsigned int VBO, VAO,EBO;
Shape m_Shape;
QOpenGLShaderProgram shaderProgram;
unsigned int texture;
QOpenGLTexture *pTexture;
QOpenGLTexture *pTexture2;
};#endif // BKQOPENGLW_H

对应cpp:

#include "bkqopenglw.h"
#include<iostream>
#include <QDebug>#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"float vertices[] = {// positions          // colors           // texture coords0.8f,  0.8f, 0.0f,   1.0f, 0.0f, 0.0f,   2.0f, 2.0f, // top right0.8f, -0.8f, 0.0f,   0.0f, 1.0f, 0.0f,   2.0f, 0.0f, // bottom right-0.8f, -0.8f, 0.0f,   0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // bottom left-0.8f,  0.8f, 0.0f,   1.0f, 1.0f, 0.0f,   0.0f, 2.0f  // top left};unsigned int indices[] = {  // note that we start from 0!0, 1, 3,  // first Triangle1, 2, 3   // second Triangle
};BKQOpenglW::BKQOpenglW(QWidget *parent) : QOpenGLWidget(parent)
{}BKQOpenglW::~BKQOpenglW()
{makeCurrent();glDeleteVertexArrays(1,&VAO);glDeleteBuffers(1,&VBO);doneCurrent();
}void BKQOpenglW::drawShapes(BKQOpenglW::Shape shape)
{m_Shape = shape;update();
}void BKQOpenglW::setWireFrame(bool b)
{makeCurrent();if(b){glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);}else {glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);}update();doneCurrent();
}void BKQOpenglW::initializeGL()
{initializeOpenGLFunctions();//    shaderProgram.addShaderFromSourceCode(QOpenGLShader::Vertex,vertexShaderSource);//    shaderProgram.addShaderFromSourceCode(QOpenGLShader::Fragment,fragmentShaderSource);shaderProgram.addShaderFromSourceFile(QOpenGLShader::Vertex,":/shader/shader.vs");shaderProgram.addShaderFromSourceFile(QOpenGLShader::Fragment,":/shader/shader.fs");shaderProgram.link();glGenVertexArrays(1, &VAO);glGenBuffers(1, &VBO);// bind the Vertex Array Object first, then bind and set vertex buffer(s), and then configure vertex attributes(s).glBindVertexArray(VAO);glBindBuffer(GL_ARRAY_BUFFER, VBO);glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);//绑定eboglBindBuffer(GL_ELEMENT_ARRAY_BUFFER,EBO);glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), nullptr);glEnableVertexAttribArray(0);glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(3 * sizeof(float)));glEnableVertexAttribArray(1);// texture coord attributeglVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(float), (void*)(6 * sizeof(float)));glEnableVertexAttribArray(2);//绑定纹理glEnable(GL_BLEND);glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);pTexture = new QOpenGLTexture(QImage(":/images/images/brickwall.jpg").mirrored());pTexture2 = new QOpenGLTexture(QImage(":/images/images/awesomeface.png").mirrored());shaderProgram.bind();shaderProgram.setUniformValue("texture1",0);shaderProgram.setUniformValue("texture2",1);// note that this is allowed, the call to glVertexAttribPointer registered VBO as the vertex attribute's bound vertex buffer object so afterwards we can safely unbindglBindBuffer(GL_ARRAY_BUFFER, 0);// You can unbind the VAO afterwards so other VAO calls won't accidentally modify this VAO, but this rarely happens. Modifying other// VAOs requires a call to glBindVertexArray anyways so we generally don't unbind VAOs (nor VBOs) when it's not directly necessary.glBindVertexArray(0);}void BKQOpenglW::resizeGL(int w, int h)
{glViewport(0,0,w,h);
}void BKQOpenglW::paintGL()
{glClearColor(0.2f, 0.3f, 0.3f, 1.0f);glClear(GL_COLOR_BUFFER_BIT);float borderColor[] = { 1.0f, 1.0f, 0.0f, 1.0f };shaderProgram.bind();glBindVertexArray(VAO);switch (m_Shape) {case Triangle:glDrawArrays(GL_TRIANGLES,0,3);break;case Rect:pTexture->bind(0);pTexture2->bind(1);//默认为GL_REPEAT 重复 GL_MIRRORED_REPEAT镜像  GL_CLAMP_TO_EDGE 边缘拉伸 GL_CLAMP_TO_BORDER 超出部分使用用户定义glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,GL_REPEAT);  // we want to repeat the awesomeface pattern so we kept it at GL_REPEATglTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,GL_REPEAT);
//        glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, borderColor);glDrawElements(GL_TRIANGLES,6,GL_UNSIGNED_INT,0);break;default:break;}}

纹理过滤(Texture Filtering)

GL_NEAREST(Nearest Neighbor Filtering，邻近过滤) 是一种OpenGL默认的纹理过滤方式。当设置为 GL_NEAREST 的时候， OpenGL选择最接近纹理坐标中心点的那个像素。下图你
会看到四个像素，加号代表纹理坐标。左上角的纹理像素是距离纹理坐标最近的那个，这样它就会选择这个作为采样颜色：

GL_LINEAR((Bi)linear Filtering，线性过滤) 它会从纹理坐标的临近纹理像素进行计算，返
回一个多个纹理像素的近似值。一个纹理像素距离纹理坐标越近，那么这个纹理像素对最终
的采样颜色的影响越大。下面你会看到临近像素返回的混合颜色：

基本区别：

使用方式：

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

最后的话：

每天写代码时间不多，上班时间还是比较长，写博客不易，喜欢的朋友，可以关注偶。