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RenderTarget Shader wrong coordinates — Gideros Forum
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    RenderTarget Shader wrong coordinates

    YanYan Member
    edited March 2021 in Bugs and issues
    There is a wrong detect of coordinates in Shader of Bitmap that uses RenderTarget. Ive write a simple shader that colors only a quarter of Bitmap, it works fine if I use Bitmap with Texture, but it fails if I use RenderTarget as Texture. To be clear I added project and GIF with explanation of this behavior.

    As you can see, for different size RenderTarget proportions GLSL Shader detects 0.5 coordinate wrong. Why this happend and how to fix this ?

    primitive Shader
    	void main() {
		vec4 vertex = vec4(vVertex, 1.0);
		gl_Position = vMatrix*vertex;
		fTexCoord = vTexCoord;
	}
    void main()
	{
		gl_FragColor = vec4(0.0, 0.0, 0.0, 0.5);
 
		if (fTexCoord.y > 0.5 && fTexCoord.x > 0.5)
		{	
			gl_FragColor = vec4(1.0, 0.5, 0.2, 0.5);
		}		
	}
    image

    vk.com/yan_alex
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    Comments

    • keszeghkeszegh Member
      i think it may be due to the shader texture being a power of two size.
      try a rendertarget of size that is a power of two, like 1024x1024. if that is fine, then this is the issue. there are some constants which can help you to get the right value even if it's not a power of two, @hgy29 knows better, he helped me out once with this, but i don't remember anymore the details (and it would take a lot of time to dig up my code now).
      Longtitle Productions, creator of
      Fragmenter - animated loop machine and IKONOMIKON - the memory game
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    • YanYan Member
      keszegh said:

      i think it may be due to the shader texture being a power of two size.
      try a rendertarget of size that is a power of two, like 1024x1024. if that is fine, then this is the issue. there are some constants which can help you to get the right value even if it's not a power of two, @hgy29 knows better, he helped me out once with this, but i don't remember anymore the details (and it would take a lot of time to dig up my code now).

      Yes, Ive already tried, and this is seems really problem of power of 2, I figured this out before started topic, but It still looks like a bug and I dont understand how to fix.

      Ive tried to multiply on ratio proportion coefficient, but I failed or this is not the solve.

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    • keszeghkeszegh Member
      edited March 2021
      it is not really a bug, just a technical limitation. under the hood every texture is of size power of two, and shader uses that.

      here is the computation i use to normalize:
      varying mediump vec2 fTexCoord;
uniform mediump vec4 fTextureInfo;
 
....
 
coord.y=(fTexCoord.y/fTextureInfo.y-0.5);	
coord.x=(fTexCoord.x/fTextureInfo.x-0.5)/fTextureInfo.z*fTextureInfo.x*fTextureInfo.w/fTextureInfo.y;
      (perhaps it is overcomplicated, also it has those 0.5's as i wanted to put the (0,0) coordinate in the middle of my texture for symmetry reasons.)
      Longtitle Productions, creator of
      Fragmenter - animated loop machine and IKONOMIKON - the memory game
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    • hgy29hgy29 Maintainer
      Yes, as @keszegh said it is due to Gideros enlarging texture sizes so that they always have a power of two size, so the 'payload' of the texture doesn't always span for 0 to 1. This is something your shader code should be aware of, and it can be helped by the constant Gideros can provide to the shader. The x and y parts of this vector are the real extent of the texture.
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    • YanYan Member
      edited March 2021
      hgy29 said:

      Yes, as @keszegh said it is due to Gideros enlarging texture sizes so that they always have a power of two size, so the 'payload' of the texture doesn't always span for 0 to 1. This is something your shader code should be aware of, and it can be helped by the constant Gideros can provide to the shader. The x and y parts of this vector are the real extent of the texture.

      What should I provide as a constant ? Im not quite really understand the solve

      Is this a part I need to provide ?


      shader:setConstant("fTexelSize",Shader.CFLOAT4,1,{1/texw,1/texh,0,0})
      and then multiply by fTexelSize.xy
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    • hgy29hgy29 Maintainer
      Accepted Answer
      Just change your condition to:
      		if (fTexCoord.y > fTexSize.y/2.0 && fTexCoord.x > fTexSize.x/2.0)

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    • YanYan Member
      Doh, I realised everybody just use UV as coord / size
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