UE4采样纹理指定位置颜色

极坐标

float polar_coordinates(float2 uvs) {
	struct SF {
		static float remap_value_range(float input, float input_low, float input_high, float target_low, float target_high) {
			return (input - input_low) / (input_high - input_low) * (target_high - target_low) + target_low;
		}
	};
	float pi = acos(-1);
	float2 uv = float2(SF::remap_value_range(uvs.x, 0, 1, -1, 1), SF::remap_value_range(uvs.y, 0, 1, -1, 1));
	return SF::remap_value_range(atan2(uv.x, uv.y) / pi, -1, 1, 0, 1);
}

旋转

/**
* 旋转
* rotation_center - 旋转点
* rotation_angle - 旋转角度
*/
float2 rotate(float2 uvs, float2 rotation_center, float rotation_angle) {
	float pi = acos(-1);
	rotation_angle *= 2 * pi;
	// 逆时针旋转
	float2x2 mt = float2x2(
		cos(rotation_angle), sin(rotation_angle),
		-sin(rotation_angle), cos(rotation_angle)
	);
	/** 顺时针旋转
	float2x2 mt = float2x2(
		cos(rotation_angle), -sin(rotation_angle),
		sin(rotation_angle), cos(rotation_angle)
	);
	*/
	return mul(uvs + rotation_center * -1, mt) + rotation_center;
}

也可以使用 UE 自带的 CustomRotator 材质函数。

溶解

/**
* 溶解
* texture2d - 纹理
* texture2d_noise - 噪点纹理
* value - 溶解程度
* edge - 溶解边缘
*     xyz - 溶解边缘颜色
*     w - 溶解边缘宽度
*/
float4 dissolve(float2 uvs, Texture2D texture2d, float2 uvs_noise Texture2D texture2d_noise, float value, float4 edge) {
	float3 texture_color = Texture2DSampleLevel(texture2d, texture2dSampler, uvs, 0).xyz;
	// float3 texture_color = Texture2DSample(texture2d, Material.Texture2D_0Sampler, uvs).xyz;
	float noise_value = Texture2DSampleLevel(texture2d_noise, texture2d_noiseSampler, uvs_noise, 1).x;
	// float noise_value = Texture2DSample(texture2d_noise, Material.Texture2D_1Sampler, uvs_noise).x;
	value = saturate(value) * 2 - 1 + noise_value;
	float dissolve_value = value * step(value, 1) * step(saturate(1 - edge.w), value);
	float3 dissolve_color = edge.xyz * dissolve_value;
	value = saturate(value);
	float alpha = 1 - floor(value);
	texture_color = lerp(texture_color, 0, value);
	float3 color = saturate(texture_color + dissolve_color);
	return float4(color, alpha);
}

燃烧

/**
* 燃烧
* texture2d - 纹理
* texture2d_noise - 噪点纹理
* noise_scale - 噪点尺寸
* value - 燃烧程度
* edge - 燃烧边缘
*     xyz - 燃烧边缘颜色
*     w - 燃烧边缘宽度
*/
float4 burn(float2 uvs, Texture2D texture2d, Texture2D texture2d_noise, float noise_scale, float value, float4 edge) {
	float3 texture_color = Texture2DSampleLevel(texture2d, texture2dSampler, uvs, 0).xyz;
	// float3 texture_color = Texture2DSample(texture2d, Material.Texture2D_0Sampler, uvs).xyz;
	float noise_value = Texture2DSampleLevel(texture2d_noise, texture2d_noiseSampler, uvs, 1).x * noise_scale;
	// float noise_value = Texture2DSample(texture2d_noise, Material.Texture2D_1Sampler, uvs).x * noise_scale;
	float progress = uvs.x + noise_value;
	value *= 1 + noise_scale + edge.w;
	float react_1 = step(value, progress);
	float react_2 = step(value - edge.w, progress);
	float react_3 = react_2 - react_1;
	float3 color = edge.xyz * react_3 + texture_color * react_1;
	return float4(color, react_2);
}

查找边缘

float3 find_edges(float2 uvs, Texture2D texture2d, float2 texture_size) {
	float GX[3][3] = {
		{-1, -2, -1},
		{0, 0, 0},
		{1, 2, 1}
	};
	float GY[3][3] = {
		{-1, 0, 1},
		{-2, 0, 2},
		{-1, 0, 1}
	};
	float ex = 0.f;
	float ey = 0.f;
	for(int x = -1; x <= 1; x++) {
		for (int y = -1; y <= 1; y++) {
			float2 uvs_offset = float2(uvs.x + x * texture_size.x, uvs.y + y * texture_size.y);
			float3 pixel_color = Texture2DSampleLevel(texture2d, texture2dSampler, uvs_offset, 0);
			ex += pixel_color * GX[x + 1][y + 1];
			ey += pixel_color * GY[x + 1][y + 1];
		}
	}
	return saturate(1 - (abs(ex) + abs(ey)));
}

浮雕

float3 emboss(float2 uvs, Texture2D texture2d, float2 texture_size, float value) {
	float GX[3][3] = {
		{-1, -2, -1},
		{0, 0, 0},
		{1, 2, 1}
	};
	float GY[3][3] = {
		{-1, 0, 1},
		{-2, 0, 2},
		{-1, 0, 1}
	};
	float ex = 0.f;
	float ey = 0.f;
	for(int x = -1; x <= 1; x++) {
		for (int y = -1; y <= 1; y++) {
			float2 uvs_offset = float2(uvs.x + x * texture_size.x, uvs.y + y * texture_size.y);
			float3 pixel_color = Texture2DSampleLevel(texture2d, texture2dSampler, uvs_offset, 0);
			ex += pixel_color * GX[x + 1][y + 1];
			ey += pixel_color * GY[x + 1][y + 1];
		}
	}
	return value + ex + ey;
}

去色

float3 desaturation(float3 color) {
	float3 factor = float3(0.299, 0.587, 0.114);
	return dot(color, factor);
}

也可以使用 UE 自带的 Desaturation 表达式。

抖动

float3 shake(float2 uvs, Texture2D texture2d, Texture2D texture2d_noise, float range, float value) {
	float noise_value = Texture2DSampleLevel(texture2d_noise, texture2d_noiseSampler, float2(sin(value), cos(value)), 0).x;
	noise_value *= range;
	// 采样红色，右移
	float texture_color_r = Texture2DSampleLevel(texture2d, texture2dSampler, float2(uvs.x + noise_value, uvs.y), 1).x;
	// 采样绿色，不变
	float texture_color_g = Texture2DSampleLevel(texture2d, texture2dSampler, uvs, 1).y;
	// 采样蓝色，左移
	float texture_color_b = Texture2DSampleLevel(texture2d, texture2dSampler, float2(uvs.x - noise_value, uvs.y), 1).z;
	return float3(texture_color_r, texture_color_g, texture_color_b);
}