io: add display unit

added rendering for modes 3,4,5
also changed how memory structuring works

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

include/io/display/display.hh

@@ -0,0 +1,159 @@
+#include "memory.hh"
+#include <array>
+#include <bit>
+#include <cstdint>
+#include <sys/types.h>
+
+// NOLINTBEGIN(cppcoreguidelines-avoid-c-arrays)
+namespace matar {
+namespace display {
+static constexpr int LCD_WIDTH = 240;
+
+// there are 5 modes
+static constexpr uint N_MODES = 6;
+// there are 4 backgrounds that can be layered depending on mode
+// there is also 1 object layer
+static constexpr uint N_BACKGROUNDS = 4;
+
+static constexpr uint32_t PRAM_START = 0x5000000;
+static constexpr uint32_t VRAM_START = 0x6000000;
+static constexpr uint32_t OAM_START  = 0x7000000;
+
+template<typename T, typename = std::enable_if_t<std::is_arithmetic_v<T>>>
+struct Point {
+    T x;
+    T y;
+};
+
+struct Color {
+  public:
+    Color(uint16_t raw)
+      : red(raw & 0b11111)
+      , green(raw >> 5 & 0b11111)
+      , blue(raw >> 10 & 0b11111) {}
+
+    uint16_t read() const {
+        return (red & 0b11111) | ((green << 5) & 0b11111) |
+               ((blue << 10) & 0b11111);
+    }
+
+  private:
+    uint8_t red;
+    uint8_t green;
+    uint8_t blue;
+};
+
+struct DisplayControl {
+    struct {
+        uint8_t mode : 3;
+        int : 1; // unused
+        bool frame_select_1 : 1;
+        bool hblank_free_interval : 1;
+        bool obj_character_vram_mapping : 1;
+        bool forced_blank : 1;
+        bool screen_display_0 : 1;
+        bool screen_display_1 : 1;
+        bool screen_display_2 : 1;
+        bool screen_display_3 : 1;
+        bool screen_display_obj : 1;
+        bool window_display_0 : 1;
+        bool window_display_1 : 1;
+        bool obj_window_display : 1;
+    } value;
+
+    uint16_t read() const { return std::bit_cast<uint16_t>(value); };
+    void write(uint16_t raw) { value = std::bit_cast<decltype(value)>(raw); };
+};
+
+struct DisplayStatus {
+    struct {
+        bool vblank_flag : 1;
+        bool hblank_flag : 1;
+        bool vcounter_flag : 1;
+        bool vblank_irq_enable : 1;
+        bool hblank_irq_enable : 1;
+        bool vcounter_irq_enable : 1;
+        int : 2; // unused
+        uint8_t vcount_setting : 8;
+    } value;
+
+    uint16_t read() const { return std::bit_cast<uint16_t>(value); };
+    void write(uint16_t raw) { value = std::bit_cast<decltype(value)>(raw); };
+};
+
+struct BackgroundControl {
+    struct {
+        uint8_t priority : 2;
+        uint8_t character_base_block : 2;
+        int : 2; // unused
+        bool mosaic : 1;
+        bool colors256 : 1;
+        uint8_t screen_base_block : 5;
+        bool bg_2_3_wraparound : 1;
+        uint8_t screen_size : 2;
+    } value;
+
+    uint16_t read() const { return std::bit_cast<uint16_t>(value); };
+    void write(uint16_t raw) { value = std::bit_cast<decltype(value)>(raw); };
+};
+
+struct RotationScaling {
+    // these are all 16 bit signed "fixed point" floats
+    // shifted by 8
+    int16_t a;
+    int16_t b;
+    int16_t c;
+    int16_t d;
+
+    // following points have 28 bit signed "fixed point" floats as coords
+    // shifted by 8
+    Point<int32_t> ref;
+
+  private:
+    Point<int32_t> internal [[maybe_unused]]
+    ;
+};
+
+struct Display {
+  public:
+    using u16 = uint16_t;
+
+    Memory<0x400> pram;
+    Memory<0x18000> vram;
+    Memory<0x400> oam;
+
+    DisplayControl lcd_control;
+    DisplayStatus general_lcd_status;
+    u16 vertical_counter;
+    BackgroundControl bg_control[4];
+    Point<u16> bg0_offset;
+    Point<u16> bg1_offset;
+    Point<u16> bg2_offset;
+    Point<u16> bg3_offset;
+    RotationScaling bg2_rot_scale;
+    RotationScaling bg3_rot_scale;
+    u16 win0_horizontal_dimensions;
+    u16 win1_horizontal_dimensions;
+    u16 win0_vertical_dimensions;
+    u16 win1_vertical_dimensions;
+    u16 inside_win_0_1;
+    u16 outside_win;
+    u16 mosaic_size;
+    u16 color_special_effects_selection;
+    u16 alpha_blending_coefficients;
+    u16 brightness_coefficient;
+
+  private:
+    // 1 color is 16 bits in ARGB555 format
+    std::array<std::array<uint16_t, LCD_WIDTH>, N_BACKGROUNDS> scanline_buffers;
+
+    template<int MODE,
+             typename = std::enable_if_t<MODE == 3 || MODE == 4 || MODE == 5>>
+    void render_bitmap_mode();
+
+    template<int LAYER, typename = std::enable_if_t<LAYER >= 0 && LAYER <= 3>>
+    void render_text_layer();
+};
+}
+}
+// NOLINTEND(cppcoreguidelines-avoid-c-arrays)