Realtime Compositor: Add basic distort nodes

This patch implements the following nodes for the realtime compositor:

- Crop node.
- Flip node.
- Lens distort node.
- Rotate node.
- Transform node.
- Translate node.

Differential Revision: https://developer.blender.org/D15231

Reviewed By: Clement Foucault

source/blender/gpu/CMakeLists.txt

@@ -323,10 +323,15 @@ set(GLSL_SRC
   shaders/common/gpu_shader_common_math_utils.glsl
   shaders/common/gpu_shader_common_mix_rgb.glsl
 
+  shaders/compositor/compositor_alpha_crop.glsl
   shaders/compositor/compositor_box_mask.glsl
   shaders/compositor/compositor_convert.glsl
   shaders/compositor/compositor_ellipse_mask.glsl
+  shaders/compositor/compositor_flip.glsl
+  shaders/compositor/compositor_image_crop.glsl
+  shaders/compositor/compositor_projector_lens_distortion.glsl
   shaders/compositor/compositor_realize_on_domain.glsl
+  shaders/compositor/compositor_screen_lens_distortion.glsl
   shaders/compositor/compositor_set_alpha.glsl
   shaders/compositor/compositor_split_viewer.glsl
 
@@ -562,10 +567,15 @@ set(SRC_SHADER_CREATE_INFOS
   shaders/infos/gpu_shader_text_info.hh
   shaders/infos/gpu_srgb_to_framebuffer_space_info.hh
 
+  shaders/compositor/infos/compositor_alpha_crop_info.hh
   shaders/compositor/infos/compositor_box_mask_info.hh
   shaders/compositor/infos/compositor_convert_info.hh
   shaders/compositor/infos/compositor_ellipse_mask_info.hh
+  shaders/compositor/infos/compositor_flip_info.hh
+  shaders/compositor/infos/compositor_image_crop_info.hh
+  shaders/compositor/infos/compositor_projector_lens_distortion_info.hh
   shaders/compositor/infos/compositor_realize_on_domain_info.hh
+  shaders/compositor/infos/compositor_screen_lens_distortion_info.hh
   shaders/compositor/infos/compositor_set_alpha_info.hh
   shaders/compositor/infos/compositor_split_viewer_info.hh
 )

source/blender/gpu/shaders/compositor/compositor_alpha_crop.glsl

@@ -0,0 +1,11 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+void main()
+{
+  ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+  /* The lower bound is inclusive and upper bound is exclusive. */
+  bool is_inside = all(greaterThanEqual(texel, lower_bound)) && all(lessThan(texel, upper_bound));
+  /* Write the pixel color if it is inside the cropping region, otherwise, write zero. */
+  vec4 color = is_inside ? texture_load(input_tx, texel) : vec4(0.0);
+  imageStore(output_img, texel, color);
+}

source/blender/gpu/shaders/compositor/compositor_flip.glsl

@@ -0,0 +1,15 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+void main()
+{
+  ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+  ivec2 size = texture_size(input_tx);
+  ivec2 flipped_texel = texel;
+  if (flip_x) {
+    flipped_texel.x = size.x - texel.x - 1;
+  }
+  if (flip_y) {
+    flipped_texel.y = size.y - texel.y - 1;
+  }
+  imageStore(output_img, texel, texture_load(input_tx, flipped_texel));
+}

source/blender/gpu/shaders/compositor/compositor_image_crop.glsl

@@ -0,0 +1,7 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+void main()
+{
+  ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+  imageStore(output_img, texel, texture_load(input_tx, texel + lower_bound));
+}

source/blender/gpu/shaders/compositor/compositor_projector_lens_distortion.glsl

@@ -0,0 +1,16 @@
+#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
+
+void main()
+{
+  ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
+
+  /* Get the normalized coordinates of the pixel centers.  */
+  vec2 normalized_texel = (vec2(texel) + vec2(0.5)) / vec2(texture_size(input_tx));
+
+  /* Sample the red and blue channels shifted by the dispersion amount. */
+  const float red = texture(input_tx, normalized_texel + vec2(dispersion, 0.0)).r;
+  const float green = texture_load(input_tx, texel).g;
+  const float blue = texture(input_tx, normalized_texel - vec2(dispersion, 0.0)).b;
+
+  imageStore(output_img, texel, vec4(red, green, blue, 1.0));
+}

source/blender/gpu/shaders/compositor/compositor_screen_lens_distortion.glsl

@@ -0,0 +1,151 @@
+#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));
+}

source/blender/gpu/shaders/compositor/infos/compositor_alpha_crop_info.hh

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_alpha_crop)
+    .local_group_size(16, 16)
+    .push_constant(Type::IVEC2, "lower_bound")
+    .push_constant(Type::IVEC2, "upper_bound")
+    .sampler(0, ImageType::FLOAT_2D, "input_tx")
+    .image(0, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_img")
+    .compute_source("compositor_alpha_crop.glsl")
+    .do_static_compilation(true);

source/blender/gpu/shaders/compositor/infos/compositor_flip_info.hh

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_flip)
+    .local_group_size(16, 16)
+    .push_constant(Type::BOOL, "flip_x")
+    .push_constant(Type::BOOL, "flip_y")
+    .sampler(0, ImageType::FLOAT_2D, "input_tx")
+    .image(0, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_img")
+    .compute_source("compositor_flip.glsl")
+    .do_static_compilation(true);

source/blender/gpu/shaders/compositor/infos/compositor_image_crop_info.hh

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_image_crop)
+    .local_group_size(16, 16)
+    .push_constant(Type::IVEC2, "lower_bound")
+    .sampler(0, ImageType::FLOAT_2D, "input_tx")
+    .image(0, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_img")
+    .compute_source("compositor_image_crop.glsl")
+    .do_static_compilation(true);

source/blender/gpu/shaders/compositor/infos/compositor_projector_lens_distortion_info.hh

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_projector_lens_distortion)
+    .local_group_size(16, 16)
+    .push_constant(Type::FLOAT, "dispersion")
+    .sampler(0, ImageType::FLOAT_2D, "input_tx")
+    .image(0, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_img")
+    .compute_source("compositor_projector_lens_distortion.glsl")
+    .do_static_compilation(true);

source/blender/gpu/shaders/compositor/infos/compositor_screen_lens_distortion_info.hh

@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "gpu_shader_create_info.hh"
+
+GPU_SHADER_CREATE_INFO(compositor_screen_lens_distortion_shared)
+    .local_group_size(16, 16)
+    .push_constant(Type::VEC3, "chromatic_distortion")
+    .push_constant(Type::FLOAT, "scale")
+    .sampler(0, ImageType::FLOAT_2D, "input_tx")
+    .image(0, GPU_RGBA16F, Qualifier::WRITE, ImageType::FLOAT_2D, "output_img")
+    .compute_source("compositor_screen_lens_distortion.glsl");
+
+GPU_SHADER_CREATE_INFO(compositor_screen_lens_distortion)
+    .additional_info("compositor_screen_lens_distortion_shared")
+    .do_static_compilation(true);
+
+GPU_SHADER_CREATE_INFO(compositor_screen_lens_distortion_jitter)
+    .additional_info("compositor_screen_lens_distortion_shared")
+    .define("JITTER")
+    .do_static_compilation(true);