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  rendering a red object white  (Read 1410 times)
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Offline ~Spaceaholic
« Posted 2012-10-03 17:43:49 »

Hi Guys,
I want to make a cool invincibility power up effect for a game I am working on, It is all 2d, rendered with opengl, using sprite sheets....
the main character for the game is a bright red crab, and I would like to make him blink white when the user is using the invincibility power up... the sprite sheet is quite large already so having a secondary sprite sheet with the crab white is not really an option.... I have played a bit with setting the color in opengl via gl.glColor4f(1,1,1,1); and was wondering is there a color combination that would allow me to render the crab white(perhaps if the rgb value of the crab was already known?)? or is there another way I should go about implementing this?
Thanks


Offline Riven
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« Reply #1 - Posted 2012-10-03 17:46:15 »

As you're using OpenGL, you should use a fragment shader, where you can manipulate all colors. In your case you'd simply add RGB(0,1,1) to your crab.

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Offline davedes
« Reply #2 - Posted 2012-10-03 18:20:34 »

A fixed function approach:
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      //set environment mode to ADD
      glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_ADD);
      glColor4f(1f, 1f, 1f, 1f);

      //draw the sprite; the colors will be white but the alpha will be in tact
      image.draw(50, 50);

      //reset mode to default...
      glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

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Offline theagentd
« Reply #3 - Posted 2012-10-04 00:13:51 »

Turn the problem around! Make the original crab image white and use glColor() to make it red! Definitely the easiest approach.

Myomyomyo.
Offline Riven
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« Reply #4 - Posted 2012-10-04 00:42:36 »

Turn the problem around! Make the original crab image white and use glColor() to make it red! Definitely the easiest approach.
Yeah, that was my first idea too, then I thought the crab was probably not 100% RGB(*,0,0)

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Offline theagentd
« Reply #5 - Posted 2012-10-04 07:05:38 »

Turn the problem around! Make the original crab image white and use glColor() to make it red! Definitely the easiest approach.
Yeah, that was my first idea too, then I thought the crab was probably not 100% RGB(*,0,0)
Why does that matter?

Myomyomyo.
Offline Riven
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« Reply #6 - Posted 2012-10-04 08:02:35 »

Because then you cannot make the crab white (well, greyscale) as you'd be losing information, that cannot be added back later.

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Offline ~Spaceaholic
« Reply #7 - Posted 2012-10-05 20:30:27 »

Thanks for all the info, I ended up using davedes's approach, and it works great... I can make the crab blink any color now!
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