如何使用计时器移动顶点着色器中的点

Question

我无法弄清楚如何使用顶点着色器使用计时器为我的对象设置动画。我有一堆点位于窗口中的随机位置。我想要做的是将这些点移动到窗口的中心（即 {0.0,0.0}），然后在一个点到达窗口中心时停在那里。这是我的顶点着色器代码：

layout(location = 0) in vec2 vertexPos;

uniform mat4 P;
uniform mat4 MV;
uniform float time;

void main() {
    gl_Position = P * MV * vec4(vertexPos, 0.0, 1.0);
}

这显示了它们随机位置的所有点。我知道如何将它们移动到中心，但我不知道如何显示实际移动到中心的点。

Answer 1

在粒子的初始位置和原点之间使用mix()到lerp：

layout(location = 0) in vec2 vertexPos;

uniform mat4 P;
uniform mat4 MV;
uniform float time;

void main()
{
    vec2 dest( 0.0, 0.0 );
    vec2 curPos = mix( vertexPos, dest, time );
    gl_Position = P * MV * vec4( curPos, 0.0, 1.0 );
}

根据主机计时器将主机代码中的 time 从 0.0 更改为 1.0。

编辑：一起来：

#include <GL/glew.h>
#include <GL/freeglut.h>
#include <iostream>
#include <cstdarg>
#include <vector>
using namespace std;

struct Program
{
    static GLuint Load( const char* shader, ... )
    {
        GLuint prog = glCreateProgram();
        va_list args;
        va_start( args, shader );
        while( shader )
        {
            const GLenum type = va_arg( args, GLenum );
            AttachShader( prog, type, shader );
            shader = va_arg( args, const char* );
        }
        va_end( args );
        glLinkProgram( prog );
        CheckStatus( prog );
        return prog;
    }

private:
    static void CheckStatus( GLuint obj )
    {
        GLint status = GL_FALSE;
        if( glIsShader(obj) ) glGetShaderiv( obj, GL_COMPILE_STATUS, &status );
        if( glIsProgram(obj) ) glGetProgramiv( obj, GL_LINK_STATUS, &status );
        if( status == GL_TRUE ) return;
        GLchar log[ 1 << 15 ] = { 0 };
        if( glIsShader(obj) ) glGetShaderInfoLog( obj, sizeof(log), NULL, log );
        if( glIsProgram(obj) ) glGetProgramInfoLog( obj, sizeof(log), NULL, log );
        std::cerr << log << std::endl;
        exit( EXIT_FAILURE );
    }

    static void AttachShader( GLuint program, GLenum type, const char* src )
    {
        GLuint shader = glCreateShader( type );
        glShaderSource( shader, 1, &src, NULL );
        glCompileShader( shader );
        CheckStatus( shader );
        glAttachShader( program, shader );
        glDeleteShader( shader );
    }
};

#define GLSL(version, shader) "#version " #version "\n" #shader

const char* vert = GLSL
(
    330 core,
    layout( location = 0 ) in vec2 vertexPos;
    uniform float time;
    void main()
    {
        vec2 dest = vec2( 0.0, 0.0 );
        vec2 curPos = mix( vertexPos, dest, time );
        gl_Position = vec4( curPos, 0.0, 1.0 );
    }
);

const char* frag = GLSL
(
    330 core,
    out vec4 color;
    void main()
    {
        color = vec4( 1.0, 1.0, 1.0, 1.0 );
    }
);

float rnd( const float lo, const float hi )
{
    return lo + ( hi - lo ) * ( rand() / (float)RAND_MAX );
}

GLuint prog = 0;
GLint timeLoc = -1;
void init()
{
    GLuint vao = 0;
    glGenVertexArrays( 1, &vao );
    glBindVertexArray( vao );

    std::vector< float > verts;
    for( size_t i = 0; i < 100; ++i )
    {
        verts.push_back( rnd( -1, 1 ) );
        verts.push_back( rnd( -1, 1 ) );
    }

    GLuint vbo = 0;
    glGenBuffers( 1, &vbo );
    glBindBuffer( GL_ARRAY_BUFFER, vbo );
    glBufferData( GL_ARRAY_BUFFER, sizeof( float ) * verts.size(), &verts[0], GL_STATIC_DRAW );

    glVertexAttribPointer( 0, 2, GL_FLOAT, GL_FALSE, 0, 0 );
    glEnableVertexAttribArray( 0 );

    prog = Program::Load
        (
        vert, GL_VERTEX_SHADER,
        frag, GL_FRAGMENT_SHADER,
        NULL
        );
    glUseProgram( prog );
    timeLoc = glGetUniformLocation( prog, "time" );
}

float u = 0.0f;
void timer( int value )
{
    const int duration = 3000;
    static int startTime = glutGet( GLUT_ELAPSED_TIME );
    const int curTime = glutGet( GLUT_ELAPSED_TIME );

    if( curTime > startTime + duration )
    {
        startTime = curTime;
    }

    u  = ( curTime - startTime ) / (float)duration;

    glutTimerFunc( 16, timer, 0 );
    glutPostRedisplay();
}

void display()
{
    glClear( GL_COLOR_BUFFER_BIT );
    glUniform1f( timeLoc, u );
    glDrawArrays( GL_POINTS, 0, 100 );
    glutSwapBuffers();
}

int main(int argc, char **argv)
{
    glutInit( &argc, argv );
    glutInitContextVersion( 3, 3 );
    glutInitContextProfile( GLUT_CORE_PROFILE );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
    glutInitWindowSize( 600, 600 );
    glutCreateWindow( "GLUT" );

    glewExperimental = GL_TRUE;
    glewInit();

    init();

    glutDisplayFunc( display );
    glutTimerFunc( 0, timer, 0 );
    glutMainLoop();
    return 0;
}