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POHow can I use a Shader in XNA to color single pixels?
 

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  1. POHow can I use a Shader in XNA to color single pixels?
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    <p>I have a standard 800x600 window in my XNA project. My goal is to color each individual pixel based on a rectangle array which holds boolean values. Currently I am using a 1x1 Texture and drawing each sprite in my array.</p> <p>I am very new to XNA and come from a GDI background, so I am doing what I would have done in GDI, but it doesn't scale very well. I have been told in another question to use a Shader, but after much research, I still haven't been able to find out how to accomplish this goal.</p> <p>My application loops through the X and Y coordinates of my rectangular array, does calculations based on each value, and reassigns/moves the array around. At the end, I need to update my "Canvas" with the new values. A smaller sample of my array would look like:</p> <pre><code>0,0,0,0,0,0,0 0,0,0,0,0,0,0 0,0,0,0,0,0,0 1,1,1,1,1,1,1 1,1,1,1,1,1,1 </code></pre> <p>How can I use a shader to color each pixel?</p> <p>A very simplified version of the calculations would be:</p> <pre><code> for (int y = _horizon; y &gt;= 0; y--) // _horizon is my ending point { for (int x = _width; x &gt;= 0; x--) // _width is obviously my x length. { if (grains[x, y] &gt; 0) { if (grains[x, y + 1] == 0) { grains[x, y + 1] = grains[x, y]; grains[x, y] = 0; } } } } </code></pre> <p>..each time the update method is called, the calculations are performed and in example of the above loop, an update may look like:</p> <p>Initial:</p> <pre><code>0,0,0,1,0,0,0 0,0,0,0,0,0,0 0,0,0,0,0,0,0 1,1,1,0,1,1,1 1,1,1,1,1,1,1 </code></pre> <p>First:</p> <pre><code>0,0,0,0,0,0,0 0,0,0,1,0,0,0 0,0,0,0,0,0,0 1,1,1,0,1,1,1 1,1,1,1,1,1,1 </code></pre> <p>Second:</p> <pre><code>0,0,0,0,0,0,0 0,0,0,0,0,0,0 0,0,0,1,0,0,0 1,1,1,0,1,1,1 1,1,1,1,1,1,1 </code></pre> <p>Final:</p> <pre><code>0,0,0,0,0,0,0 0,0,0,0,0,0,0 0,0,0,0,0,0,0 1,1,1,1,1,1,1 1,1,1,1,1,1,1 </code></pre> <p>Update:</p> <p>After applying the Render2DTarget code and placing my pixels, I end up with an unwanted border on my pixels, always to the left. How can I remove this?</p> <p><a href="http://www.refuctored.com/borders.png" rel="nofollow noreferrer">alt text http://www.refuctored.com/borders.png</a></p> <p><a href="http://www.refuctored.com/fallingdirt.png" rel="nofollow noreferrer">alt text http://www.refuctored.com/fallingdirt.png</a></p> <p>The some of the code for applying the textures is:</p> <pre><code> RenderTarget2D target; Texture2D texture; protected override void LoadContent() { spriteBatch = new SpriteBatch(GraphicsDevice); texture = Content.Load&lt;Texture2D&gt;("grain"); _width = this.Window.ClientBounds.Width - 1; _height = this.Window.ClientBounds.Height - 1; target = new RenderTarget2D(this.GraphicsDevice,_width, _height, 1, SurfaceFormat.Color,RenderTargetUsage.PreserveContents); } protected override void Draw(GameTime gameTime) { this.GraphicsDevice.SetRenderTarget(0, target); this.GraphicsDevice.SetRenderTarget(0, null); this.GraphicsDevice.Clear(Color.SkyBlue); this.spriteBatch.Begin(SpriteBlendMode.None,SpriteSortMode.Deferred,SaveStateMode.None); SetPixels(texture); this.spriteBatch.End(); } private void SetPixels(Texture2D texture) { for (int y = _grains.Height -1; y &gt; 0; y--) { for (int x = _grains.Width-1; x &gt; 0; x--) { if (_grains.GetGrain(x, y) &gt;0) { this.spriteBatch.Draw(texture, new Vector2(x,y),null, _grains.GetGrainColor(x, y)); } } } } </code></pre>
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    1. USDanny Varod
    1. USGeorge Johnston
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      1. POHow can I use a Shader in XNA to color single pixels?
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      1. POHow can I use a Shader in XNA to color single pixels?
      1. USsmack0007
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      1. POHow can I use a Shader in XNA to color single pixels?
      1. USGeorge Johnston
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    1. COWould you mind sharing the calculations you perform on your rectangular array? If you can do those calculations inside the shader it may not be too hard to figure out. I'm having trouble figuring out how to pass an array of size 800x600 to the shader because arrays are limited to 65536 indices (16-bit index), apparently; so if you could just perform the calculations inside the shader without having to pass the large array in each time it would be easier to figure out.
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      1. POHow can I use a Shader in XNA to color single pixels?
      1. USVenesectrix
    2. COI've updated the question with some more supporting information for your inquiry.
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      1. POHow can I use a Shader in XNA to color single pixels?
      1. USGeorge Johnston
    3. COActually, sorry, now that I think about it that approach isn't a good idea for a number of reasons. It requires that a texture represent the initial state of your array, the pixel shader can't modify the texture, it can only return different values, so each time it was called it would be like starting from the initial state, and it does all the calculations in the draw() function instead of the update() function, which is probably not a good idea.
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      1. POHow can I use a Shader in XNA to color single pixels?
      1. USVenesectrix
 

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