16
May
08

to fade in and fade out….

With regards to the programming behind my final piece I was not happy with the way in which the two videos switched when the sensor was triggered.  The change was very abrupt as the videos quite literally flipped, with no fluidity, so I set about working out how to program my patch to blend the two videos when a presence was sensed.

I had already implemented a horizontal slider which switched from left to right when the sensor triggered, far left being the video that plays when no presence is sensed  and far right being the video that plays when a presence is sensed.  A bang message is sent to the slider when the sensor is triggered thus changing the visuals (a bang message is also sent when the sensor returns to its idle position flipping the source back into its original state)

When the sliders properties were set to default (left = 0, right = 127) there was no blending affect.  With a little research on the Pure Data forums I found that I needed to change the values to left 0.01 and right 1, with these new values a blending affect was achieved, albeit when I dragged the slider by hand.  What I needed now was to program the slider to move automatically when the sensor was triggered.

As Pure Data is just numbers I needed a counter send messages to the slider telling it what value to use at specific points in time (for example, if the values were left = 1 right = 10, I would need a counter to send the slider the number 1 then 2, 3, 4, 5, 6, 7, 8, 9, 10, this would move the slider from left to right as each of the numbers were received) 

The way I found to do this was to set a metro (metros send bang messages at a rate in milliseconds, so if you set the metro at 500, it will send a bang every half a second) So in theory I wanted to counter to start at 0.01 (far left) and for the metro to send a new number incrementally every 25 milliseconds until it reached 1 (far right) unfortunately this was not so straight forward.  For some reason the even though the counter was counting the correct values, the slider was not receiving them and therefore it was not moving in a fluid manner, quite the contrary actually, the slider jumped form far left to far right, with the correct delay that I had set in total (0.25 of a second) but ignoring the values in-between.  Obviously this was not what I wanted as the videos still abruptly flipped two and from one another.  I tested the counter with the default slider values and adjusted the math accordingly and the slider smoothly drifted from left to right!? I couldn’t use these values because they did not achieve the fade a was after.  By now I was getting confused, the maths were the same (in principal) but the affect was the opposite.

I decided to average out the numbers using an average object.  The average object (as the name implies) averages the numbers between two variables by a number that you set (for example, if left = 1 and right = 10 and I set the average object to 20, it would divide 10 into 20 and count accordingly, i.e. it would count 0.5, 1, 1.5, 2 and so on until it reached 10)  I thought that as the difference between the numbers I needed to use (0.01 – 1) was so small (in comparison to 1 – 127) the counter slider was ignoring the decimals in-between and only acknowledging the whole numbers (0 -1)  I used the average object to divide the difference between 0.01 and 1 by 50 and told the slider to listen to that object over everything else, and it worked! kind of…

By averaging the numbers and programming the slider in this way I achieved a smooth transition from left to right, but another problem arose.  The average object needed to have a reset message sent to it after everytime it was triggered, otherwise it wouldn’t work again.  To get around this I outputted the sliders values into numbers and used a moses object.  The moses object sends a bang message when ever a value that you set is reached.  I set the moses object to send a bang to the reset message whenever it received the value of 1, this reset the average object and thus the process could be repeated again.  The only thing left to do was to reverse this entire process so as the videos would fade out as well as fade in and Volia!  it was done…… (phew)  The image below show the final counter patch.  


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