Adds first draft of an interface to separate CRT logic from the GPU-side stuff.

Outputs/CRT/CRT.hpp

@@ -27,6 +27,52 @@ class Delegate {
 		virtual void crt_did_end_batch_of_frames(CRT *crt, unsigned int number_of_frames, unsigned int number_of_unexpected_vertical_syncs) = 0;
 };
 
+struct ScanTarget {
+	struct Modals {
+		enum class DataType {
+			Luminance1,				// 1 byte/pixel; any bit set => white; no bits set => black.
+			Luminance8,				// 1 byte/pixel; linear scale.
+
+			Phase4Luminance4,		// 1 byte/pixel; top nibble is a phase offset, bottom nibble is luminance.
+			Phase8Luminance8,		// 1 bytes/pixel; first is phase, second is luminance.
+
+			Red1Green1Blue1,		// 1 byte/pixel; bit 0 is blue on or off, bit 1 is green, bit 2 is red.
+			Red2Green2Blue2,		// 1 byte/pixel; bits 0 and 1 are blue, bits 2 and 3 are green, bits 4 and 5 are blue.
+			Red4Green4Blue4,		// 2 bytes/pixel; first nibble is red, second is green, third is blue.
+			Red8Green8Blue8,		// 4 bytes/pixel; first is red, second is green, third is blue, fourth is vacant.
+		} source_data_type;
+		ColourSpace colour_space;
+	};
+	virtual void set_modals(Modals);
+
+	struct EndPoint {
+		uint32_t data_offset;
+		uint16_t x, y;
+		uint16_t phase;
+		uint8_t amplitude;
+	};
+	EndPoint *get_endpoint_pair();
+
+	/// Finds the first available space of at least @c required_length pixels in size which is suitably aligned
+	/// for writing of @c required_alignment number of pixels at a time.
+	/// Calls must be paired off with calls to @c reduce_previous_allocation_to.
+	/// @returns a pointer to the allocated space if any was available; @c nullptr otherwise.
+	virtual uint8_t *allocate_write_area(std::size_t required_length, std::size_t required_alignment = 1) = 0;
+
+	/// Announces that the owner is finished with the region created by the most recent @c allocate_write_area
+	/// and indicates that its actual final size was @c actual_length.
+	virtual void reduce_previous_allocation_to(std::size_t actual_length) = 0;
+
+	virtual void submit() = 0;
+	virtual void reset() = 0;
+
+	enum class Event {
+		HorizontalSync,
+		VerticalSync
+	};
+	virtual void announce(Event event) = 0;
+};
+
 class CRT {
 	private:
 		CRT(unsigned int common_output_divisor, unsigned int buffer_depth);