SE TTIN G UP DIFFER ENT CA MERA MODE S IN YOUR 3 D WORLD in Word

Generate DataMatrix in Word SE TTIN G UP DIFFER ENT CA MERA MODE S IN YOUR 3 D WORLD

Recipe 4-17 in 4 explains in detail how to find the rotation angle corresponding to a direction. In this case, you have to find two angles because the direction is in 3D. Start by finding the leftrightRot angle. Figure 2-5 shows the XZ plane containing the camera and the target. The diagonal line is the direction the camera is facing, and the X and Z lines are simply the X and Z components of that vector. In a triangle with a 90-degree angle, if you want to find the angle of a corner, all you need to do is take the arctangent of the side opposite the corner, divided by the shortest side next to the corner. In this case, this comes down to X divided by Z. The Atan2 function allows you to specify both values instead of their division, because this removes an ambiguity. This is how you find the leftrightRot angle.

Figure 2-5. Finding the leftrightRot angle To find the updownAngle, you can use Figure 2-6. Here, the dashed line shows the direction the camera is looking. You want to find the angle between the Up Y component and the projection of the direction on the XZ floor plane. So, you pass these to the Atan2 method, and you receive the updownAngle.

Make sure you call your UpdateBezier method from your Update method: UpdateBezier(); Now all you have to do to start a fly-by is call the InitBezier method! if (bezTime > 1.0f) InitBezier(new Vector3(0,10,0), new Vector3(0,0,0), new Vector3(0, 0, -20), new Vector3(0, 0, -10)); When you want to integrate your fly-by with your user camera, you can start from your camera s position and target easily: if (bezTime > 1.0f) InitBezier(fpsCam.Position, fpsCam.Position + fpsCam.Forward * 10.0f, new Vector3(0, 0, -20), new Vector3(0, 0, -10)); You can see I have placed the starting target 10 units in front of the starting position. This will often give a smoother result, because otherwise the camera would have to make a sharp turn when tracking the target.

By constantly increasing the bezTime from 0 to 1 by a fixed amount, the speed at which the camera moves over the Bezier curve is a constant. This will result in a rather uncomfortable starting and ending. What you really want is to have the bezTime first rise slowly from 0 to 0.2 and then rise pretty fast to 0.8, while slowing down again during the last part between 0.8 and 1. This is exactly what MathHelper.SmoothStep does: you give it a constantly increasing value between 0 and 1, and it will return a value between 0 and 1 that has a smooth starting and ending! The only place where you need this is in the UpdateBezier method, so replace the middle two lines with this code: float smoothValue = MathHelper.SmoothStep(0, 1, bezTime); Vector3 newCamPos = Bezier(bezStartPosition, bezMidPosition, bezEndPosition, smoothValue); Vector3 newCamTarget = Vector3.Lerp(bezStartTarget, bezEndTarget, smoothValue); The smoothValue variable will hold this smoothed value between 0 and 1, which will be passed to the methods, instead of the constantly increasing bezTime variable.

This part of the recipe addresses a problem that can occur in some cases. One of such cases is shown in the left part of Figure 2-7, where the path of the camera position and the curve of the target is shown from above. In the beginning, the camera will be looking to the left, until both curves cross. At this point, the camera will suddenly be switched, so it is looking to the right! You can correct this situation by simply shifting the midpoint of the curve to the left, instead of to the right. This way, you get a curve as shown in the right part, where the starting camera will start by looking to the right and doesn t have to be switched to the left.