mrt-drop-shadow.hlsl

uniform float4x4 ViewProj;
//this pulls in the texture from render target 1
uniform texture2d image;
//assuming the pattern followed~
uniform texture2d image_2;
uniform texture2d image_3;

uniform float2 elapsed_time;
uniform float2 uv_offset;
uniform float2 uv_scale;
uniform float2 uv_pixel_interval;

uniform float shadow_x;
uniform float shadow_y;

uniform float blur_size;

uniform float4 shadow_color;

sampler_state textureSampler {
	Filter    = Linear;
	AddressU  = Border;
	AddressV  = Border;
	BorderColor = 00000000;
};

struct VertData {
	float4 pos : POSITION;
	float2 uv  : TEXCOORD0;
};

VertData mainTransform(VertData v_in)
{
	VertData vert_out;
	vert_out.pos = mul(float4(v_in.pos.xyz, 1.0), ViewProj);
	vert_out.uv = v_in.uv * uv_scale + uv_offset;
	return vert_out;
}

struct PS_OUTPUT
{
	float4 color: SV_Target0;
	float4 original: SV_Target1;
	float4 shadow: SV_TARGET2;
};

PS_OUTPUT drop_shadow_init(VertData v_in)
{
	PS_OUTPUT output;	
	float4 c = image.Sample(textureSampler, v_in.uv);
	output.original = c;
	output.color = c;
	output.shadow = float4(shadow_color.rgb, c.a);
	
	return output;
}

PS_OUTPUT drop_shadow_blur_x(VertData v_in)
{
	PS_OUTPUT output;
	
	int shadow_blur_samples = (shadow_blur_size * 2) + 1;
	
	float2 shadow_uv = float2(v_in.uv.x - uv_pixel_interval.x * shadow_offset_x, 
						  v_in.uv.y - uv_pixel_interval.y * shadow_offset_y);
	
	float sampled_shadow_alpha = 0;
	
	for (int blur_i = -shadow_blur_size; blur_i <= shadow_blur_size; blur_i++){
		float2 blur_uv = shadow_uv + float2(0, uv_pixel_interval.y * blur_i);
		sampled_shadow_alpha += image.Sample(textureSampler, blur_uv).a;
	}
	
	sampled_shadow_alpha /= shadow_blur_samples;
	
	output.color = float4(shadow_color.rgb, shadow_color.a * sampled_shadow_alpha);
	output.original = image_2;
	output.shadow = output.color;
}

PS_OUTPUT drop_shadow_blur_y(VertData v_in)
{
	PS_OUTPUT output;
	
	int shadow_blur_samples = (shadow_blur_size * 2) + 1;
	
	float2 shadow_uv = float2(v_in.uv.x - uv_pixel_interval.x * shadow_offset_x, 
						  v_in.uv.y - uv_pixel_interval.y * shadow_offset_y);
	
	float4 sampled_shadow = float4(0,0,0,0);
	
	for (int blur_i = -shadow_blur_size; blur_i <= shadow_blur_size; blur_i++){
		float2 blur_uv = shadow_uv + float2(uv_pixel_interval.x * blur_i, 0);
		sampled_shadow += image_3.Sample(textureSampler, blur_uv);
	}
	
	sampled_shadow /= shadow_blur_samples;
	
	float4 original_color = image_2.Sample(textureSampler, v_in.uv);
	output.shadow = sampled_shadow;
	output.color = sampled_shadow * (1-original_color.a) + original_color * (is_alpha_premultiplied * 1 + !is_alpha_premultiplied * original_color.a);
	output.original_color = original_color;
}

technique Draw
{
	pass p0
	{
		vertex_shader = mainTransform(v_in);
		pixel_shader = drop_shadow_init(v_in);
	}
	
	pass p2
	{
		vertex_shader = mainTransform(v_in);
		pixel_shader = drop_shadow_blur_x(v_in);
	}
	
	pass p3
	{
		vertex_shader = mainTransform(v_in);
		pixel_shader = drop_shadow_blur_y(v_in);
	}
}