Build view-space light cluster grid in a compute pass

gl/cluster_grid.h

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+#pragma once
+
+#include <glm/glm.hpp>
+
+#include "ssbo.h"
+#include "ubo.h"
+#include "shader.h"
+
+namespace gl
+{
+	// GPU resources of the light cluster grid of one viewport. the grid cuts the view frustum of a pass into
+	// CLUSTER_GRID_X x CLUSTER_GRID_Y screen tiles and CLUSTER_GRID_Z slices of depth, spaced exponentially
+	// between znear and zfar (layout and binding points: ubo.h). depth is the clip space w of a point, which is
+	// also 1.0 / gl_FragCoord.w of its fragment and, unlike the view space z, is right for tilted screens.
+	// the buffers have a fixed size, so the grid survives changes of the resolution, fov and draw range: those
+	// only make its parameters and boxes be recomputed.
+	// bindings of the buffers are context state and the buffers are per viewport, so bind() has to be done in
+	// the context and before every pass which uses the grid
+	class cluster_grid
+	{
+	  public:
+		cluster_grid();
+
+		void bind();
+
+		// refreshes the parameters for a pass: its projection, depth range and the size of the render target.
+		// returns true if the boxes of the clusters no longer match them and build() has to run
+		bool update(const glm::mat4 &projection, float znear, float zfar, glm::vec2 viewport_size);
+		// recomputes the boxes of the clusters in view space with the program made from cluster_build.comp.
+		// binds the grid, and leaves the boxes ready to be read by the compute passes which follow
+		void build(program &build_program);
+
+		// false if the last update found no grid possible for the pass (orthographic projection)
+		bool valid() const
+		{
+			return m_params.valid != 0;
+		}
+		const cluster_ubs &params() const
+		{
+			return m_params;
+		}
+
+	  private:
+		// cluster_aabb per cluster
+		ssbo m_aabbs;
+		// cluster_range per cluster
+		ssbo m_ranges;
+		// light indices of all clusters, allocated from m_counters.index_count
+		ssbo m_indices;
+		// cluster_counters
+		ssbo m_counters;
+		ubo m_params_buffer;
+
+		cluster_ubs m_params{};
+		bool m_boxes_stale = true;
+	};
+} // namespace gl