DragonRuby Game Toolkit - Hot-loaded shaders while retaining game state. (https://youtu.be/pc7Jj6c9pNs)

assets.md

effect.frag.hlsl

Texture2D scene : register(t0);
Texture2D displacement_map : register(t1);
SamplerState sampler0 : register(s0);

struct Input {
    float4 tex_color : COLOR0;
    float2 tex_coord : TEXCOORD0;
};

struct Output {
    float4 frag_color : SV_Target;
};

Output main(Input input) {
  Output output;
  float4 tex1_color = displacement_map.Sample(
    sampler0,
    input.tex_coord
  );

  float displacement_perc = 0.02;

  float2 displacement_uv = float2(
    input.tex_coord.x + (tex1_color.r * displacement_perc - displacement_perc / 2.0),
    input.tex_coord.y + (tex1_color.r * displacement_perc - displacement_perc / 2.0)
  );
  float2 resolved_displacement_uv = float2(
    clamp(displacement_uv.x, 0.0, 1.0),
    clamp(displacement_uv.y, 0.0, 1.0)
  );
  float4 tex0_color = scene.Sample(sampler0, resolved_displacement_uv);
  output.frag_color = tex0_color;
  return output;
}

main.rb

def tick args
  args.outputs[:water].set w: 1280, h: 720, background_color: [255, 255, 255]
  args.outputs[:water].primitives << 3.map do |i|
    sprite_size = 720
    [
      {
        x: 0,
        y: Grid.h / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water.png",
        a: 128,
      },
      {
        x: 720,
        y: Grid.h / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water.png",
        a: 128,
      },
      {
        x: Grid.w / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        y: 0,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water.png",
        a: 128,
      },
    ]
  end

  args.outputs[:displacement].set w: 1280, h: 720, background_color: [255, 255, 255]
  args.outputs[:displacement].primitives << 3.map do |i|
    sprite_size = 720
    [
      {
        x: Grid.w / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        y: 0,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water-displacement.png",
        a: 128
      },
      {
        x: 0,
        y: Grid.h / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water-displacement.png",
        a: 128
      },
      {
        x: 720,
        y: Grid.h / 2 - i * sprite_size + Kernel.tick_count % sprite_size,
        w: sprite_size, h: sprite_size,
        path: "sprites/flow-like-water/water-displacement.png",
        a: 128
      }
    ]
  end

  args.outputs.shader = {
    path: "shaders/effect.frag.hlsl",
    textures: [
      :displacement
    ]
  }

  args.outputs.primitives << { x: 0, y: 0, w: 1280, h: 720, path: :water }
  args.outputs.primitives << { x: args.state.tick_count % 1280,
                               y: args.state.tick_count % 720,
                               text: "flow like water",
                               anchor_x: 0.5,
                               anchor_y: 0.5,
                               size_px: 100,
                               r: 1,
                               g: 1,
                               b: 1 }

  args.outputs.primitives << { x: args.inputs.mouse.x,
                               y: args.inputs.mouse.y,
                               w: 64, h: 64,
                               path: "sprites/square/blue.png",
                               anchor_x: 0.5 , anchor_y: 0.5 }
end