我需要在帧上绘制小圆圈,并使它们在几帧后消失(淡出)。如何使用 OpenGL ES 实现这一目标?
这是我目前所拥有的,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。 谢谢
最佳答案
您将需要在每一帧上重新渲染所有对象(圆圈)。所以你需要保留一个数据结构来保存关于圆的信息(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,你迭代圆的数组,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()
函数可以是你上面写的:
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);
}
关于objective-c - 如何处理openGL中几个圆圈的淡出?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/11484314/