OpenGL shader use

The shader is OpenGL Important concepts in , Is running on the GPU The applet on

1. Vertex shader

#version 330 core
layout (location=0) in vec3 aPos;
out vec4 vertextColor;
void main(){
    
	gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
	vertextColor = vec4(1.0, 1.0, 0.0, 1.0);
}

#version 330 core
Current version and openGL The version number of corresponds to

layout (location=0) in vec3 aPos;
location Set the attribute position value of the position variable of external input data , The external data is shown above aPos The location variable attribute value of is 0.in Indicates input , out Indicative output
aPos Define a variable input position coordinates

gl_Position yes GLSL Internal keywords , be used for GPU Position display of
gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0); Receive coordinates from external input

out vec4 vertextColor; Define colors in vertex shaders , You can wear it all the way to the clip shader . Just define the same variable reception in the fragment shader

2. Fragment Shader

#version 330 core
out vec4 fragColor;
in vec4 vertextColor;// Color passed from vertex shader 
void main(){
    
	//fragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);

	fragColor = vertextColor;
}

Be careful ： Each vertex shader can only have one output variable ！！！

3. from CPU towards GPU Transmit data

Use keywords in shaders uniform
Defined in shaders

uniform vec4 randColor;

GLuint randColor = _shaderProgram.uniformLocation("randColor");
	_shaderProgram.setUniformValue(randColor, QVector4D(0.4, qAbs(qSin((float)time.elapsed()/1000.0)),0.3 ,1.0));

4. Code example

#pragma once

#include <QOpenGLWindow>
#include <QOpenGLShader>
#include <QOpenGLShaderProgram>
#include <QTime>
class QOpenGLFunctions_3_3_Core;


class HelloShader : public QOpenGLWindow {
    
	Q_OBJECT

public:
	HelloShader();
	~HelloShader();

private:
	void initializeGL();
	void resizeGL(int w, int h);
	void paintGL();

private:
	QOpenGLFunctions_3_3_Core* _openGLCore;
	GLuint _VBO;
	GLuint _VAO;
	QOpenGLShaderProgram _shaderProgram;// Shader program , All shaders in the system 
	QTime time = QTime::currentTime();
};

#include "HelloShader.h"
#include <QOpenGLFunctions_3_3_Core>
#include <QVector4D>
#include <QMath.h>

HelloShader::HelloShader() {
    
}

HelloShader::~HelloShader() {
    
}

void HelloShader::initializeGL() {
    
	_openGLCore = QOpenGLContext::currentContext()->versionFunctions<QOpenGLFunctions_3_3_Core>();

	GLfloat ver[] = {
    
		// If there are two triangles , Conventional drawing method , Define the position points of two triangles 
		// The first triangle 
		0.0f,  0.5f, 0.0f,
	   -0.5f, -0.5f, 0.0f,
		0.5f, -0.5f, 0.0f,
	};

	_openGLCore->glGenBuffers(1, &_VAO);
	_openGLCore->glBindVertexArray(_VAO);

	_openGLCore->glGenBuffers(1, &_VBO);
	_openGLCore->glBindBuffer(GL_ARRAY_BUFFER, _VBO);
	_openGLCore->glBufferData(GL_ARRAY_BUFFER, sizeof(ver), ver, GL_STATIC_DRAW);
	_openGLCore->glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (void*)0);

	_openGLCore->glEnableVertexAttribArray(0);

	_openGLCore->glBindVertexArray(0);


	QOpenGLShader vertexShager(QOpenGLShader::Vertex);// Vertex shader 
	vertexShager.compileSourceFile("E:/Projects/QtGuiTest/OPenGLApp/shader/HelloShader.vert");
	QOpenGLShader fragmentShager(QOpenGLShader::Fragment);// Fragment Shader 
	fragmentShager.compileSourceFile("E:/Projects/QtGuiTest/OPenGLApp/shader/HelloShader.frag");
	_shaderProgram.addShader(&vertexShager);
	_shaderProgram.addShader(&fragmentShager);

	_shaderProgram.link();
}

void HelloShader::resizeGL(int w, int h) {
    

}

void HelloShader::paintGL() {
    
	_openGLCore->glClearColor(0.6f, 0.6f, 0.6f, 1.0);
	_openGLCore->glClear(GL_COLOR_BUFFER_BIT);

	_shaderProgram.bind();

	GLuint randColor = _shaderProgram.uniformLocation("randColor");
	_shaderProgram.setUniformValue(randColor, QVector4D(0.4, qAbs(qSin((float)time.elapsed()/1000.0)),0.3 ,1.0));
	
	_openGLCore->glBindVertexArray(_VAO);



	_openGLCore->glDrawArrays(GL_TRIANGLES, 0, 3);

	update();
}

Vertex shader ：

#version 330 core
layout (location=0) in vec3 aPos;
out vec4 vertextColor;
void main(){
    
	gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
	vertextColor = vec4(1.0, 1.0, 0.0, 1.0);
}

Fragment Shader

#version 330 core
out vec4 fragColor;
in vec4 vertextColor;// Color passed from vertex shader 

uniform vec4 randColor;
void main(){
    
	//fragColor = vec4(1.0f, 0.5f, 0.2f, 1.0f);

	//fragColor = vertextColor;
	fragColor = randColor;
}

Running results ：

above ！
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