two-pass-drop-shadow.shader

uniform float4x4 ViewProj;
uniform texture2d image;

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

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;
}

uniform int shadow_offset_x;
uniform int shadow_offset_y;
uniform int shadow_blur_size;

uniform float4 shadow_color;

uniform bool is_alpha_premultiplied;

float4 mainImage(VertData v_in) : TARGET
{
    int shadow_blur_samples = shadow_blur_size + 1;//pow(shadow_blur_size * 2 + 1, 2);
    
    float4 color = image.Sample(textureSampler, v_in.uv);
    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_x = -shadow_blur_size; blur_x <= shadow_blur_size; blur_x++)
    {
		float2 blur_uv = shadow_uv + float2(uv_pixel_interval.x * blur_x, 0);
		sampled_shadow_alpha += image.Sample(textureSampler, blur_uv).a;
    }
	
	sampled_shadow_alpha /= shadow_blur_samples;
    
    float4 final_shadow_color = float4(shadow_color.rgb, shadow_color.a * sampled_shadow_alpha);
    
    return final_shadow_color * (1-color.a) + color * (is_alpha_premultiplied * 1 + !is_alpha_premultiplied * color.a);
}

float4 mainImage_2_end(VertData v_in) : TARGET
{
    int shadow_blur_samples = shadow_blur_size + 1;//pow(shadow_blur_size * 2 + 1, 2);
    
    float4 color = image.Sample(textureSampler, v_in.uv);
    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_y = -shadow_blur_size; blur_y <= shadow_blur_size; blur_y++)
    {
		float2 blur_uv = shadow_uv + float2(0, uv_pixel_interval.y * blur_y);
		sampled_shadow_alpha += image.Sample(textureSampler, blur_uv).a;
    }
	
	sampled_shadow_alpha /= shadow_blur_samples;
    
    float4 final_shadow_color = float4(shadow_color.rgb, shadow_color.a * sampled_shadow_alpha);
    
    return final_shadow_color * (1-color.a) + color * (is_alpha_premultiplied * 1 + !is_alpha_premultiplied * color.a);
}

technique Draw
{
	pass p0
	{
		vertex_shader = mainTransform(v_in);
		pixel_shader = mainImage(v_in);
	}
	
	pass p1
	{
		vertex_shader = mainTransform(v_in);
		pixel_shader = mainImage_2_end(v_in);
	}
}