使用下面的代码，我从不同大小的三角形条中绘制线条。在最后一个三角形的点，我想添加一个 GLpoint 基元，这样它看起来就像这条线有一个圆形的末端。如何根据最终三角形的大小计算 GLpoint 的正确直径？请参阅所附图片，展示我目前拥有的东西（这个点太大了）。
- (void)pan:(UIPanGestureRecognizer *)p {
CGPoint v = [p velocityInView:self.view];
CGPoint l = [p locationInView:self.view];
float distance = sqrtf((l.x - previousPoint.x) * (l.x - previousPoint.x) + (l.y - previousPoint.y) * (l.y - previousPoint.y));
float velocityMagnitude = sqrtf(v.x*v.x + v.y*v.y);
float clampedVelocityMagnitude = clamp(VELOCITY_CLAMP_MIN, VELOCITY_CLAMP_MAX, velocityMagnitude);
float normalizedVelocity = (clampedVelocityMagnitude - VELOCITY_CLAMP_MIN) / (VELOCITY_CLAMP_MAX - VELOCITY_CLAMP_MIN);
float lowPassFilterAlpha = STROKE_WIDTH_SMOOTHING;
float newThickness = (STROKE_WIDTH_MAX - STROKE_WIDTH_MIN) * normalizedVelocity + STROKE_WIDTH_MIN;
penThickness = penThickness * lowPassFilterAlpha + newThickness * (1 - lowPassFilterAlpha);
glBindVertexArrayOES(vertexArrayTriangles);
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferTriangles);
if ([p state] == UIGestureRecognizerStateBegan)
{
previousPoint = l;
previousMidPoint = l;
NISignaturePoint startPoint = {
{ (l.x / self.view.bounds.size.width * 2. - 1), ((l.y / self.view.bounds.size.height) * 2.0 - 1) * -1, 0}, {0,0,0}
};
previousVertex = startPoint;
previousThickness = penThickness;
addVertexTriangles(&lengthTriangles, startPoint);
addVertexTriangles(&lengthTriangles, previousVertex);
} else if ([p state] == UIGestureRecognizerStateChanged) {
CGPoint mid = CGPointMake((l.x + previousPoint.x) / 2.0, (l.y + previousPoint.y) / 2.0);
if (distance > QUADRATIC_DISTANCE_TOLERANCE) {
// Plot quadratic bezier instead of line
unsigned int i;
int segments = (int) distance / 1.5;
float startPenThickness = previousThickness;
float endPenThickness = penThickness;
previousThickness = penThickness;
for (i = 0; i < segments; i++)
{
penThickness = startPenThickness + ((endPenThickness - startPenThickness) / segments) * i;
double t = (double)i / (double)segments;
double a = pow((1.0 - t), 2.0);
double b = 2.0 * t * (1.0 - t);
double c = pow(t, 2.0);
double x = a * previousMidPoint.x + b * previousPoint.x + c * mid.x;
double y = a * previousMidPoint.y + b * previousPoint.y + c * mid.y;
NISignaturePoint v = {
{
(x / self.view.bounds.size.width * 2. - 1),
((y / self.view.bounds.size.height) * 2.0 - 1) * -1,
0
},
strokeColor
};
[self addTriangleStripPointsForPrevious:previousVertex next:v];
previousVertex = v;
}
}
previousPoint = l;
previousMidPoint = mid;
}
else if (p.state == UIGestureRecognizerStateEnded | p.state == UIGestureRecognizerStateCancelled)
{
addVertexTriangles(&lengthTriangles, previousVertex);
addVertexTriangles(&lengthTriangles, previousVertex);
glBindVertexArrayOES(vertexArrayPoints);
glBindBuffer(GL_ARRAY_BUFFER, vertexBufferPoints);
NISignaturePoint startPoint = {
{previousVertex.vertex.x, previousVertex.vertex.y, 0}, strokeColor, ???
};
addVertexPoints(&lengthPoints, startPoint);
penThickness = STROKE_WIDTH_MIN;
previousThickness = penThickness;
}
}
- (void)addTriangleStripPointsForPrevious:(NISignaturePoint)previous next:(NISignaturePoint)next {
float toTravel = penThickness / 2.0;
//NSLog(@"add tri");
for (int i = 0; i < 2; i++) {
GLKVector3 p = perpendicular(previous, next);
GLKVector3 p1 = next.vertex;
GLKVector3 ref = GLKVector3Add(p1, p);
float distance = GLKVector3Distance(p1, ref);
float difX = p1.x - ref.x;
float difY = p1.y - ref.y;
float ratio = -1.0 * (toTravel / distance);
difX = difX * ratio;
difY = difY * ratio;
NISignaturePoint stripPoint = {
{ p1.x + difX, p1.y + difY, 0.0 },
strokeColor
};
addVertexTriangles(&lengthTriangles, stripPoint);
toTravel *= -1;
}
}
