Show a sprite being hit like in the arcades.

SinisterSoft · July 2019

Ok, so sometimes you shouldn't believe everything you read.

For example, in the Gideros instructions it says that the setColorTransform command takes parameters from the value 0 to 1. That's kinda not true.

But, it's a useful 'not true' as it means you can add a nice effect used in arcade games for when a sprite gets hit. In an arcade game they usually flash white.

Normally you would have to have a white 'mask' of the sprite or do some fancy shader coding, but in reality you don't because the setColorTransform limit is actually not 1...

Here is my game sprite:

Here is code that has a much higher than 'valid' value for the setColorTransform...

Want to make it red instead? ...

So, it's that easy! After a frame just set the transform back to normal (1,1,1) and the original colours will be restored.

SinisterSoft · July 2019

btw, Sorry I didn't mention this trick earlier, I thought most people knew about it - a friend was just discussing how they were having to make a shader to do this exact same thing - so I thought I'd let you all know.

hgy29 · July 2019

Actually, it may work or not depending on the GPU...

SinisterSoft · July 2019

Seems to work on most things.

(everything I've tried)

Apollo14 · October 2019

Hi guys! That was very nice quick tip, thx!

I have one similar question: how to fill whole sprite with definite RGB or hex color?

temp_sprite:setColorTransform(46, 204, 113, 1) --it doesn't work (I've tried to multiply/divide it too)

Apollo14 · October 2019

p.s. uh, I partially got this working
if my temp_sprite is 100% white, I can fill it with colors:

temp_sprite:setColorTransform(46/255, 204/255, 113/255, 1)

Now how to fill non-white pictures with color? It has something to do with blending?

MoKaLux · October 2019

what effect are you trying to achieve, make the whole body the same color? Have you tried https://wiki.giderosmobile.com/index.php/Media ?

keszegh · October 2019

you can set up a simple shader to do that, if nothing else works.

Apollo14 · October 2019

MoKaLux said:
what effect are you trying to achieve, make the whole body the same color? Have you tried https://wiki.giderosmobile.com/index.php/Media ?

I want to simply fill multi-colored sprites with one plain color:

If sprite is white, this code works:

temp_sprite:setColorTransform(46/255, 204/255, 113/255, 1)

But if sprite is multi-colored, it doesn't work.

Apollo14 · October 2019

I guess it can be done with blending?
http://forum.giderosmobile.com/discussion/6742/2016-10-sprite-setblendmode-src-dst

http://docs.giderosmobile.com/reference/gideros/Sprite/setBlendMode#Sprite:setBlendMode
http://wiki.giderosmobile.com/index.php/Sprite:setBlendMode

But either I am stupid or it's not documented enough for noobs like me, I've no idea how to do even simple stuff, how to actually use them blendmodes and rendertarget.

MoKaLux · October 2019

@Apollo14
It seems that most of the values do not work, the wiki page seems very outdated?
The only values I could get are:

-- set blend mode
application:setBackgroundColor(0x121212)
local mysprite = Sprite.new()
local mybitmap = Bitmap.new(Texture.new("gfx/enemy01.png"))
local mypixel = Pixel.new(0x00ff00, 1, 30, 30)
mysprite:addChild(mybitmap)
mysprite:addChild(mypixel)
 
mysprite:setBlendMode(Sprite.ADD)
--mysprite:setBlendMode(Sprite.ALPHA)
--mysprite:setBlendMode(Sprite.MULTIPLY)
--mysprite:setBlendMode(Sprite.NO_ALPHA)
--mysprite:setBlendMode(Sprite.SCREEN)
stage:addChild(mysprite)

hgy29 · October 2019

setColorTransform alone can’t do that, because it multiplies the texture color by whatever you passed in parameters. So it will give what you expected only if the texture color is 1,1,1 (white).
A custom shader would do the job easily, as @keszegh suggested.

MoKaLux · October 2019

thank you for your insight. Every shaders seem to be custom shaders

At my level I would have gone the render target way but it may be slow for what you are doing!

BTW I had a last try you can experiment with:

-- set blend mode
application:setBackgroundColor(0x0055aa)
local mysprite = Sprite.new()
local mybitmap = Bitmap.new(Texture.new("gfx/enemy01.png"))
local mybitmap2 = Bitmap.new(Texture.new("gfx/enemy01.png"))
--mybitmap2:setColorTransform(255/255, 255/255, 255/255, 1)
mysprite:addChild(mybitmap)
mysprite:addChild(mybitmap2)
 
mysprite:setBlendMode(Sprite.ADD) -- bright color
--mysprite:setBlendMode(Sprite.ALPHA)
--mysprite:setBlendMode(Sprite.MULTIPLY) -- dark color
--mysprite:setBlendMode(Sprite.NO_ALPHA)
--mysprite:setBlendMode(Sprite.SCREEN)
stage:addChild(mysprite)

hgy29 · October 2019

Actually there could be way using alpha blending operators I think. The idea would be to ignore source color and use destination color in combination with source alpha:
a) Fill your target area with the color you want your sprite to be in
b) draw your sprite with blending factors ZERO for source and SRC_ALPHA for destination

I didn't try but in theory that should work

hgy29 · October 2019

It was a bit trickier than I thought, because Gideros doesn't output pixels with 0 alpha values, but with the help of stencil it can be done:

local star=Bitmap.new(Texture.new("star.png",true))
stage:addChild(star)
 
local bluestar_tex=RenderTarget.new(star:getWidth(),star:getHeight())
local bluestar=Bitmap.new(bluestar_tex)
stage:addChild(bluestar) bluestar:setX(160)
 
--Here is the magic
-- Clear our render target to all alpha
bluestar_tex:clear(0x000000,0)
--[[Gideros don't draw pixels with alpha value of 0, 
they are discarded at early stage. Use the stencil to get a
footprint of visible pixels of source image]]
star:setStencilOperation{ stencilClear=true, stencilWriteMask=1,
	stencilFunc=Sprite.STENCIL_ALWAYS,depthPass=Sprite.STENCIL_INCR }
bluestar_tex:draw(star)
--Render the footprint in the color we want
local mask=Pixel.new(0x0000FF,1,star:getWidth(),star:getHeight())
mask:setStencilOperation{ stencilClear=false, stencilMask=1, stencilWriteMask=1, 
	stencilRef=0, stencilFunc=Sprite.STENCIL_NOTEQUAL,
	depthPass=Sprite.STENCIL_KEEP,
	stencilFail=Sprite.STENCIL_KEEP}
bluestar_tex:draw(mask)
 
--[[ The result is possibly enough here, but we lost the smoothed edges of
the original texture in the process. We can restore them with a smart alpha
blending trick:]]
star:setBlendMode(Sprite.ZERO,Sprite.SRC_ALPHA)
bluestar_tex:draw(star)
 
--Restore our initial bitmap blending mode, to show it on screen as usual
star:setBlendMode(Sprite.ALPHA)

MoKaLux · October 2019

works perfectly, the only problem is understanding the code

Apollo14 · October 2019

Thank you guys!! You're awesome!!
I'll try to understand it after morning meditation when my mind is fresh

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Show a sprite being hit like in the arcades.

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Show a sprite being hit like in the arcades.

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