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Diffstat (limited to 'source/blender/compositor/realtime_compositor/shaders/compositor_screen_lens_distortion.glsl')
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diff --git a/source/blender/compositor/realtime_compositor/shaders/compositor_screen_lens_distortion.glsl b/source/blender/compositor/realtime_compositor/shaders/compositor_screen_lens_distortion.glsl
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+++ b/source/blender/compositor/realtime_compositor/shaders/compositor_screen_lens_distortion.glsl
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+#pragma BLENDER_REQUIRE(gpu_shader_common_hash.glsl)
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+/* A model that approximates lens distortion parameterized by a distortion parameter and dependent
+ * on the squared distance to the center of the image. The distorted pixel is then computed as the
+ * scalar multiplication of the pixel coordinates with the value returned by this model. See the
+ * compute_distorted_uv function for more details. */
+float compute_distortion_scale(float distortion, float distance_squared)
+{
+ return 1.0 / (1.0 + sqrt(max(0.0, 1.0 - distortion * distance_squared)));
+}
+
+/* A vectorized version of compute_distortion_scale that is applied on the chromatic distortion
+ * parameters passed to the shader. */
+vec3 compute_chromatic_distortion_scale(float distance_squared)
+{
+ return 1.0 / (1.0 + sqrt(max(vec3(0.0), 1.0 - chromatic_distortion * distance_squared)));
+}
+
+/* Compute the image coordinates after distortion by the given distortion scale computed by the
+ * compute_distortion_scale function. Note that the function expects centered normalized UV
+ * coordinates but outputs non-centered image coordinates. */
+vec2 compute_distorted_uv(vec2 uv, float scale)
+{
+ return (uv * scale + 0.5) * texture_size(input_tx) - 0.5;
+}
+
+/* Compute the number of integration steps that should be used to approximate the distorted pixel
+ * using a heuristic, see the compute_number_of_steps function for more details. The numbers of
+ * steps is proportional to the number of pixels spanned by the distortion amount. For jitter
+ * distortion, the square root of the distortion amount plus 1 is used with a minimum of 2 steps.
+ * For non-jitter distortion, the distortion amount plus 1 is used as the number of steps */
+int compute_number_of_integration_steps_heuristic(float distortion)
+{
+#if defined(JITTER)
+ return distortion < 4.0 ? 2 : int(sqrt(distortion + 1.0));
+#else
+ return int(distortion + 1.0);
+#endif
+}
+
+/* Compute the number of integration steps that should be used to compute each channel of the
+ * distorted pixel. Each of the channels are distorted by their respective chromatic distortion
+ * amount, then the amount of distortion between each two consecutive channels is computed, this
+ * amount is then used to heuristically infer the number of needed integration steps, see the
+ * integrate_distortion function for more information. */
+ivec3 compute_number_of_integration_steps(vec2 uv, float distance_squared)
+{
+ /* Distort each channel by its respective chromatic distortion amount. */
+ vec3 distortion_scale = compute_chromatic_distortion_scale(distance_squared);
+ vec2 distorted_uv_red = compute_distorted_uv(uv, distortion_scale.r);
+ vec2 distorted_uv_green = compute_distorted_uv(uv, distortion_scale.g);
+ vec2 distorted_uv_blue = compute_distorted_uv(uv, distortion_scale.b);
+
+ /* Infer the number of needed integration steps to compute the distorted red channel starting
+ * from the green channel. */
+ float distortion_red = distance(distorted_uv_red, distorted_uv_green);
+ int steps_red = compute_number_of_integration_steps_heuristic(distortion_red);
+
+ /* Infer the number of needed integration steps to compute the distorted blue channel starting
+ * from the green channel. */
+ float distortion_blue = distance(distorted_uv_green, distorted_uv_blue);
+ int steps_blue = compute_number_of_integration_steps_heuristic(distortion_blue);
+
+ /* The number of integration steps used to compute the green channel is the sum of both the red
+ * and the blue channel steps because it is computed once with each of them. */
+ return ivec3(steps_red, steps_red + steps_blue, steps_blue);
+}
+
+/* Returns a random jitter amount, which is essentially a random value in the [0, 1] range. If
+ * jitter is not enabled, return a constant 0.5 value instead. */
+float get_jitter(int seed)
+{
+#if defined(JITTER)
+ return hash_uint3_to_float(gl_GlobalInvocationID.x, gl_GlobalInvocationID.y, seed);
+#else
+ return 0.5;
+#endif
+}
+
+/* Each color channel may have a different distortion with the guarantee that the red will have the
+ * lowest distortion while the blue will have the highest one. If each channel is distorted
+ * independently, the image will look disintegrated, with each channel seemingly merely shifted.
+ * Consequently, the distorted pixels needs to be computed by integrating along the path of change
+ * of distortion starting from one channel to another. For instance, to compute the distorted red
+ * from the distorted green, we accumulate the color of the distorted pixel starting from the
+ * distortion of the red, taking small steps until we reach the distortion of the green. The pixel
+ * color is weighted such that it is maximum at the start distortion and zero at the end distortion
+ * in an arithmetic progression. The integration steps can be augmented with random values to
+ * simulate lens jitter. Finally, it should be noted that this function integrates both the start
+ * and end channels in reverse directions for more efficient computation. */
+vec3 integrate_distortion(int start, int end, float distance_squared, vec2 uv, int steps)
+{
+ vec3 accumulated_color = vec3(0.0);
+ float distortion_amount = chromatic_distortion[end] - chromatic_distortion[start];
+ for (int i = 0; i < steps; i++) {
+ /* The increment will be in the [0, 1) range across iterations. */
+ float increment = (i + get_jitter(i)) / steps;
+ float distortion = chromatic_distortion[start] + increment * distortion_amount;
+ float distortion_scale = compute_distortion_scale(distortion, distance_squared);
+
+ /* Sample the color at the distorted coordinates and accumulate it weighted by the increment
+ * value for both the start and end channels. */
+ vec2 distorted_uv = compute_distorted_uv(uv, distortion_scale);
+ vec4 color = texture(input_tx, distorted_uv / texture_size(input_tx));
+ accumulated_color[start] += (1.0 - increment) * color[start];
+ accumulated_color[end] += increment * color[end];
+ }
+ return accumulated_color;
+}
+
+void main()
+{
+ ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+
+ /* Compute the UV image coordinates in the range [-1, 1] as well as the squared distance to the
+ * center of the image, which is at (0, 0) in the UV coordinates. */
+ vec2 center = texture_size(input_tx) / 2.0;
+ vec2 uv = scale * (texel + 0.5 - center) / center;
+ float distance_squared = dot(uv, uv);
+
+ /* If any of the color channels will get distorted outside of the screen beyond what is possible,
+ * write a zero transparent color and return. */
+ if (any(greaterThan(chromatic_distortion * distance_squared, vec3(1.0)))) {
+ imageStore(output_img, texel, vec4(0.0));
+ return;
+ }
+
+ /* Compute the number of integration steps that should be used to compute each channel of the
+ * distorted pixel. */
+ ivec3 number_of_steps = compute_number_of_integration_steps(uv, distance_squared);
+
+ /* Integrate the distortion of the red and green, then the green and blue channels. That means
+ * the green will be integrated twice, but this is accounted for in the number of steps which the
+ * color will later be divided by. See the compute_number_of_integration_steps function for more
+ * details. */
+ vec3 color = vec3(0.0);
+ color += integrate_distortion(0, 1, distance_squared, uv, number_of_steps.r);
+ color += integrate_distortion(1, 2, distance_squared, uv, number_of_steps.b);
+
+ /* The integration above performed weighted accumulation, and thus the color needs to be divided
+ * by the sum of the weights. Assuming no jitter, the weights are generated as an arithmetic
+ * progression starting from (0.5 / n) to ((n - 0.5) / n) for n terms. The sum of an arithmetic
+ * progression can be computed as (n * (start + end) / 2), which when subsisting the start and
+ * end reduces to (n / 2). So the color should be multiplied by 2 / n. The jitter sequence
+ * approximately sums to the same value because it is a uniform random value whose mean value is
+ * 0.5, so the expression doesn't change regardless of jitter. */
+ color *= 2.0 / vec3(number_of_steps);
+
+ imageStore(output_img, texel, vec4(color, 1.0));
+}