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POiOS OpenGLES2.0 drawing point at correct size
 

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    <p>Using the code below I am drawing lines from triangle strips of varying sizes. At the point of the final triangle I would like to add a GLpoint primitive so it looks like the line has a rounded end. How would I calculate the correct diameter for the GLpoint based upon the size of the final triangle? Please see attached image demonstrating what I have at the moment (the point is much too large).</p> <p><img src="https://i.stack.imgur.com/WtOvt.png" alt="enter image description here"></p> <pre><code> - (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(&amp;lengthTriangles, startPoint); addVertexTriangles(&amp;lengthTriangles, previousVertex); } else if ([p state] == UIGestureRecognizerStateChanged) { CGPoint mid = CGPointMake((l.x + previousPoint.x) / 2.0, (l.y + previousPoint.y) / 2.0); if (distance &gt; 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 &lt; 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(&amp;lengthTriangles, previousVertex); addVertexTriangles(&amp;lengthTriangles, previousVertex); glBindVertexArrayOES(vertexArrayPoints); glBindBuffer(GL_ARRAY_BUFFER, vertexBufferPoints); NISignaturePoint startPoint = { {previousVertex.vertex.x, previousVertex.vertex.y, 0}, strokeColor, ??? }; addVertexPoints(&amp;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 &lt; 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(&amp;lengthTriangles, stripPoint); toTravel *= -1; } } </code></pre>
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