Question

这学期，我正在学校上一门计算机图形学课程，我们的第一个任务是创造一个凹凸幻觉。

这是我应该创建的示例：

我尝试自己解决此问题，但是我一直陷于困境。我知道如何创建灰色背景，也知道如何创建圆。我不知道该怎么办，是使圆圈看起来像图片。我知道如何用纯色填充它，我只是不知道如何用多种颜色填充它并像图片中那样淡化它。

这是我们在Visual Studio 15中运行的C ++代码。

#include <cstdlib>
#include <glut.h>
#include <math.h>

const double p = 3.14159/180;

void circle(float r){
     glColor3f(1.0,0.0,0.0);
     glBegin(GL_LINE_LOOP);
     for (int i=100; i <= 460; i++){
         double degree = p*i;
         double x = cos(degree) * r;
         double y = sin(degree) * r;
         glVertex2d(x,y);
     }
     glEnd();
}

/*

//This circle function was my attempt at creating the illusion shown in the picture above.
//I tried to break up the circle into separate pieces and make them each a different color,
//but unfortunately it didnt come out like the picture above.

void circle (float radius){
     glColor3f(0.0,0.0,0.0); // black
     glBegin(GL_POLYGON);
        glVertex2i(21,21);
        glVertex2i(25,19);
        glVertex2i(28,17);
        glVertex2i(32,16);
        glVertex2i(36,17);
        glVertex2i(40,19);
        glVertex2i(43,21);
     glEnd();
     glColor3f(0.329412,0.329412,0.329412);  // dim grey
     glBegin(GL_POLYGON);
        glVertex2i(21,21);
        glVertex2i(19,25);
        glVertex2i(17,30);
        glVertex2i(48,30);
        glVertex2i(46,25);
        glVertex2i(43,21);
     glEnd();
     glColor3f(0.752941,0.752941,0.752941);  // grey
     glBegin(GL_POLYGON);
        glVertex2i(17,30);
        glVertex2i(16,35);
        glVertex2i(15,40);
        glVertex2i(50,40);
        glVertex2i(49,35);
        glVertex2i(48,30);
     glEnd();
     glColor3f(0.650024,0.650024,0.650024);  // light grey
     glBegin(GL_POLYGON);
        glVertex2i(15,40);
        glVertex2i(16,45);
        glVertex2i(17,50);
        glVertex2i(48,50);
        glVertex2i(49,45);
        glVertex2i(50,40);
     glEnd();
     glColor3f(0.8,0.8,0.8);  //  very light grey
     glBegin(GL_POLYGON);
        glVertex2i(17,50);
        glVertex2i(20,55);
        glVertex2i(45,55);
        glVertex2i(48,50);
     glEnd();
     glColor3f(1.0,1.0,1.0);  // white
     glBegin(GL_POLYGON);
        glVertex2i(20,55);
        glVertex2i(23,58);
        glVertex2i(25,60);
        glVertex2i(28,62);
        glVertex2i(32,63);
        glVertex2i(36,62);
        glVertex2i(40,60);
        glVertex2i(43,58);
        glVertex2i(45,55);
     glEnd();
}

*/


void display(void){
     glClear(GL_COLOR_BUFFER_BIT);
     glColor3f(0.658824,0.658824,0.658824);
     glBegin(GL_POLYGON); //Creates the gray background
        glVertex2i(10,10);
        glVertex2i(390, 10);
        glVertex2i(390,290);
        glVertex2i(10,290);
     glEnd();
     circle(30);
     glFlush();
}



void main(int argc, char** argv){
     glutInit(&argc, argv);
     glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
     glutInitWindowSize(400, 300);
     glutInitWindowPosition(200,100);
     glutCreateWindow("Project 1");
     glClearColor(0.0,0.0,0.0,0.0);
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     gluOrtho2D(0.0,400.0,0.0,300.0);
     glutDisplayFunc(display);
     glutMainLoop();
}

因此，我把大部分代码记下来了，我只是想不出圆圈的颜色。

任何可以使我的代码结果看起来像上面的示例图片的建议/帮助将不胜感激。

谢谢！

Answer 1

按var toIterate = { name: "somename", personal: { age: "19", color: "dark" } }; console.log(getObjPath(toIterate).map(item => item.join('.'))); function isObject(x) { return Object.prototype.toString.call(x) === '[object Object]'; }; function getObjPath(obj, pathArray, busArray) { pathArray = pathArray ? pathArray : []; if (isObject(obj)) { for (key in obj) { if (obj.hasOwnProperty(key)) { if (isObject(obj[key])) { busArray = busArray ? bussArray : []; busArray.push(key); getObjPath(obj[key], pathArray, busArray); } else { if (busArray) { pathArray.push(busArray.concat([key])); } else { pathArray.push([key]); } } } } } return pathArray; } / glBegin顺序绘制已过了数年。阅读有关Fixed Function Pipeline的信息，并参阅Vertex Specification和Shader了解最新的渲染方式。

但是，图片的效果是通过简单的灰色渐变实现的。背景为灰色，圆圈内为从白色到黑色的线性颜色渐变。

glClear，用glClearColor设置的颜色清除帧缓冲区。
设置灰色透明颜色以创建灰色背景：

glEnd

要创建颜色渐变，必须先通过glColor3d设置颜色属性，然后再通过glVertex2d设置顶点坐标。颜色在顶点之间进行插值。使用primitive type glClearColor( 0.5f, 0.5f, 0.5f, 1.0f ); glClear(GL_COLOR_BUFFER_BIT);创建一个填充的多边形：

GL_TRIANGLE_FAN

const double p = 3.14159/180; void circle(float r, bool flip ){ glBegin(GL_TRIANGLE_FAN); glColor3d( 0.5, 0.5, 0.5 ); glVertex2d( 0.0, 0.0 ); for (int i=0; i <= 360; i++) { double degree = p*i; double c = cos( degree ); double s = sin( degree ); double col = s * 0.5 + 0.5; if ( flip ) col = 1.0 - col; glColor3d( col, col, col ); glVertex2d( c*r, s*r ); } glEnd(); }函数可能看起来像这样：

draw

预览：

如何在OpenGL中创建“凹/凸圆幻觉”

1 个答案: