LÖVE

Le Fauve wrote:Hi,

First of all, I'm new to Löve, to lua and to glsl shaders, so I apologize in advance if I ask something stupid .

I'm trying to achieve a simple starfield effect, and I think it should be interesting to use pixel shaders for this.
I made some tests and I'm getting there, however I do have an issue: I need to give to my shader a table of vec3.

I found in the documentation a way to do it, but it works by passing explicitly all elements of the array:

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myShader = love.graphics.newShader[[
	extern vec3 field[3]; 
.../...
]]

for i=0,599 do
	field[i] = { i+.5,2,.5 }
end
myShader:send("field",field[0],field[1],field[2]);

This is working, but my problem is that I want to pass a 600 vec3 array...

For the record, I did try to pass the 600 parameters to myShader:send(), and it fails with "Syntax error: main.lua:xx: function or expression too complex near 'field'".

Any idea how I could do that?
My search on this forum found two interesting topic on shaders, but none of them address this issue (viewtopic.php?f=4&t=78252 and viewtopic.php?f=4&t=32605).

I'm considering passing a 1x600 pixels image, but that seems a little overkill (and the only way I found for accessing a given pixel from an image is to use the Texel() function, which will require me to normalize my 0-599 index, forcing me to do an extra multiplication/pixel).
Also I'm concern that OpenGL may try to be smart and to antialias the pixel it will return if I am not straight on the center of the pixel, which would ruin the effect.

Long story short, I could really use a little push in the right direction here and I'm open to any suggestion!

myShader:send("field",unpack(field));

S0lll0s wrote: If you're passing 600 values to the shader you're probably doing something wrong already, but nevertheless this could work:

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myShader:send("field",unpack(field));

Wojak wrote:I think that in this case you don't need to send anything... (I assume that 600 is screen height)

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myShader = love.graphics.newShader[[
	vec4 effect( vec4 color, Image texture, vec2 texture_coords, vec2 screen_coords ){
		//note that GLSL counts y coordinates from the bottom of the screen so you may want to add:
		// screen_coords.y = 600- screen_coords.y;
		vec3 field = vec3(screen_coords.y+0.5,2,0.5);
		//you should be able to access the values by  field.x,  field.y and field.z
	}
]]

bizziboi wrote:I am not sure why you feel using a texture is overkill.

When you pass a texture you
a) Give the shader something it's made to work with and work with fast
b) Only use up one shader parameter slot

bizziboi wrote:When you pass 600 values
a) I think you can't do that. Are there that many parameter slots?
b) Regardless, the shader has to bind 600 elements, that's more expensive than looking up in a texture (the gfx card is made to do that and do it fast)
c) You use pretty much the same amount of data

bizziboi wrote:There's a reason people use lookup textures.

Perhaps the most common misconception about textures is that textures are pictures: images of skin, rock, or something else that you can look at in an image editor. While it is true that many textures are pictures of something, it would be wrong to limit your thoughts in terms of textures to just being pictures.

Le Fauve wrote:so my question is: What is the best way to transform a data table into an image?