WPF, canvas, visual, shader fx effects

Question

In a WPF application, I create a system.windows.media.effect to allow me change the color of a visual as red instead of the original color:

here is a example ^^^^^^^^^^^^^

it's a shader .fx effect that, when applyed to the visual object, it change any pixel that is NOT white as RED.
So , in this case, only black appears Red.

I notice that the first visual (a rectangle) added to the canvas is correctly rendered as i need, here it's:

if i add anothe visuals, the red pixel effect is applyed to the portion of another visuals too:

the question is: Why ??

the effect is appyed to only ONE object of the 3 object that are in the canvas...

How to render all the 3 rectangle as the first one ?
Anybody can have a advise ?

Thanks!

Answer 1

I have a shader SelectionEffect.fx effect like this:

sampler2D Input1 : register(S0);

float4 main(float2 uv : TEXCOORD) : COLOR
{
float4 color;
color = tex2D(Input1, uv);

if ((color.r != 1.0f) && (color.g != 1.0f) && (color.b != 1.0f)) {
    color.r = 1.0;
    color.g = 0.0;
    color.b = 0.0;
    //color.a = 0.9;
}

return color;

}

Compiled as SelectionEffect.ps and added his .cs class file, of course.

It's used to change the color of the object to red only, when I select it (activate a property according in the object), instead of assigned a tempoaraneally red color to the object.
I would to use this solution that is faster, i have 50-100 thousand objects.

So,to assign this effect at the object that i have already added to canvas is only:

((System.Windows.Shapes.Path)shape.Visual).Effect = new MyShaders.SelectionEffect();

to remove it:

((System.Windows.Shapes.Path)shape.Visual).Effect = null;

Please note that in the example I'm applyed this "effect" to one object pro time, so, it's intended that i would change color of the only object that have "effect" applyed in that moment and not to the anothers.

Using:

((System.Windows.Shapes.Path)shape.Visual).Stroke = new SolidColorBrush(Colors.Red);

is slow.

Answer 2

I try to explaine it as simple as i can:

I use the "Path" Object added to a canvas:

https://learn.microsoft.com/it-it/dotnet/api/system.windows.shapes.path?view=net-5.0

to this object, i apply a effect (https://learn.microsoft.com/it-it/dotnet/api/system.windows.uielement.effect?view=net-5.0#System_Windows_UIElement_Effect):

mypathobject.effect = new MyShaders.SelectionEffect();

the effect is create by me using fxc compiler. the code is:

sampler2D Input1 : register(S0);

float4 main(float2 uv : TEXCOORD) : COLOR
{
float4 color;
color = tex2D(Input1, uv);

 if ((color.r != 1.0f) && (color.g != 1.0f) && (color.b != 1.0f)) {  
     color.r = 1.0;  
     color.g = 0.0;  
     color.b = 0.0;  
     //color.a = 0.9;  
 }  
 return color;  

this effect is applied when i select the object, so it become red only that object (this is what i need).

the problem is the different rendering of the red effect on the 3 added objects to canvas, as you can see on images.

is this clear ?