Question

我需要在一个帧上绘制小圆圈并让它们在几帧（淡出）后消失。如何使用OpenGL ES实现这一目标？

这就是我到目前为止在框架中绘制圆圈的代码：

 [EAGLContext setCurrentContext:context];
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glViewport(0, 0, backingWidth, backingHeight);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrthof(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f);
    glMatrixMode(GL_MODELVIEW);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    GLfloat vertices[720];

    for (int i = 0; i < 720; i += 2) {
        vertices[i]   = (cos(DEGREES_TO_RADIANS(i)) * 1);
        vertices[i+1] = (sin(DEGREES_TO_RADIANS(i)) * 1);
    }

    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(1.0f, 1.0f, 0.0f, 1.0f);

    glDrawArrays(GL_TRIANGLE_FAN, 0, 360);

    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER_OES];

我不明白的是如何跟踪同一个圆圈并在连续的帧中淡化它。感谢

Answer 1

您需要在每个帧上重新渲染所有对象（圆圈）。因此，您需要保留一个数据结构，其中包含有关圆的信息（可能它们的中心，半径和不透明度就足够了）。像这样：

typedef struct Circle {
    NSPoint center;
    float radius;
    float opacity;
} Circle;

Circle allCircles [ kMaxNumCircles ];

然后，当你去绘制它们时，你迭代圆圈阵列，更新它们的不透明度然后绘制它们：

for (int i = 0; i < kMaxNumCircles; i++)
{
    allCircles [ i ].opacity -= someDelta;
    drawCircle (allCircles [ i ]);
}

drawCircle()函数可能就是您上面所写的内容：

void drawCircle(Circle c)
{
    GLfloat vertices[720];

    for (int i = 0; i < 720; i += 2) {
        vertices[i]   = (cos(DEGREES_TO_RADIANS(i)) * 1) + c.center.x;
        vertices[i+1] = (sin(DEGREES_TO_RADIANS(i)) * 1) + c.center.y;
    }

    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glEnableClientState(GL_VERTEX_ARRAY);

    glColor4f(1.0f, 1.0f, 0.0f, c.opacity);

    glDrawArrays(GL_TRIANGLE_FAN, 0, 360);

}

如何处理openGL中几个圆圈的淡出？

1 个答案: