The ability to be able to construct an object, lets use the Candle metaphor, whereby the user can drag the object randomly over the canvas and as the object moves so it lights up the image beneath in its path as if it was shedding light over the subject below.
Useful examples i've seen are: a lantern lighting the way along a path or lighting up a room as you move around within it; a candle exposing some text on a page etc. It adds a very dramatic experience to simple activities.
Yes i have implemented what you suggest on smallish areas but that can only work in a very limited pre-conceived motion or interaction. Imagine where you have a big image of say Dracula's palace on the canvas darkened out and you want the user to explore the room... you don't know where she will drag her lantern so you have to prepare the entire canvas as small sections which you would then layer and expose different opacities over time and then additionally you have to get the user to repeat touch events to trigger the changes in opacities.
The granularity would have to be quite high to give something that is effective and at best you end up with an approximated effect after a real lot of work.
But the big issue is when they drag a lantern around, as the metaphor, then you won't be getting any touch events occurring as the lantern is dragged across the canvas... currently there is no other feedback of position of the user's finger other than Begin and End Touch events.
Thanks for the suggestion and putting it on the wish list:)
EMPLOYEE1This effect can be faked by channelling the Rolling Stones,
Step 1. Paint It Black
Make the paper background dark or black
Step 2. Paint it Black again
Make a new texture 32x32 or 64x64 depending on how big you want the flame to be, large flame 32x32 small flame 64x64. Oh and Paint It Black.
Step 3. Shine a Light
In the middle of the texture place a white circle, don't worry about it being blocky as when we stretch the image in Composer the hardware will smooth it out for us. Make the circle a lot smaller than the image, say 8x8 big.
Step 4. Let it bleed
Set the Alpha in the middle of the circle to be about 50% and then let the edges bleed back into 0
Step 5. Sticky Fingers
Place the image on your page, and scale it nice and large so the texture covers the page ( this is why a 32x32 will have a large flame and a 64x64 will have a small one ) and then enable dragging on it. Adjust the bounds to be larger like -500 to + 1500 such that its big enough to allow you to get the flame to all of the areas on the page you wish to see. But no so big you can see around the new image.
Make the white yellow or redish in tone more a fire effect. Since its only 32x32 or 64x64 you can animate it to give a flickering glow.
To make it so people can barely see what is on the page make the image's opacity in Inspector .9 or .8 so they can through it a little bit.
Thank you for taking the time out to give a thorough working tip example...
i took some time so that i could experiment with your instructions which i have now done.
Your example certainly works and is certainly a viable work around for some situations although not as effective as i would like to see in the ideal solution of a canned effect where you could do some blending of the image background using some blend functions like you get in Photoshop layer blends (hard light, vivid, lighten etc.) even flickering light with a moving flame would be really cool.
There are some excellent examples of what i was hoping to see in a future feature in the excellent Dracula interactive book by PadWorx... page 10 provides a superb draggable lit match effect, page 30 shows a draggable swinging lantern effect and page 78 a flickering candle lighting the page.
There is an example on page 69 which could be done just as you have exampled here.
So in the meantime i will look for some Red doors that i can paint black:)
We also managed to make this work by cutting a hole. In other words, make a giant black image with a soft-edged hole in it (the image must be far larger than the canvas size) and make it draggable. Dragging the "hole" around makes it seem as though you're dragging the torchlight around. Just another option.