saturn-examples/vdp1/cube2.cpp

#include <stdint.h>
#include "vdp2.h"
#include "vdp1.h"

#include <concepts>

#include "../common/vdp2_func.hpp"

#include "../math/fp.hpp"
#include "../math/vec3.hpp"
#include "../math/mat3x3.hpp"

#include "cos.hpp"

// |--
// |
// |

using vec3 = vec<3, fp16_16>;
using mat3x3 = mat<3, 3, fp16_16>;

static constexpr vec3 vertices[8] = {
  {-0.5, -0.5,  0.5}, // top left front
  { 0.5, -0.5,  0.5}, // top right front
  { 0.5,  0.5,  0.5}, // bottom right front
  {-0.5,  0.5,  0.5}, // bottom left front

  {-0.5, -0.5, -0.5}, // top left back
  { 0.5, -0.5, -0.5}, // top right back
  { 0.5,  0.5, -0.5}, // bottom right back
  {-0.5,  0.5, -0.5}, // bottom left back
};

static constexpr uint32_t faces[6][4] = {
  {0, 1, 2, 3}, // front clockwise
  {5, 4, 7, 6}, // back clockwise
  {0, 4, 5, 1}, // top clockwise
  {3, 2, 6, 7}, // bottom clockwise
  {4, 0, 3, 7}, // left clockwise
  {1, 5, 6, 2}, // right clockwise
};

consteval vec3 normal(int32_t ix)
{
  const uint32_t * face = faces[ix];
  vec3 a = vertices[face[1]] - vertices[face[0]];
  vec3 b = vertices[face[3]] - vertices[face[0]];
  //return vertices[face[0]] + cross(a, b);
  return cross(a, b);
}

static constexpr vec3 normals[6] = {
  normal(0),
  normal(1),
  normal(2),
  normal(3),
  normal(4),
  normal(5),
};

struct canvas {
  fp16_16 width;
  fp16_16 height;
};

constexpr struct canvas canvas = { 240, 240 };

template <typename T>
vec<3, T> viewport_to_canvas(T x, T y)
{
  return vec<3, T>(x * canvas.width, y * canvas.height, T(1));
}

template <typename T>
inline constexpr vec<3, T> project_vertex(vec<3, T> const& v)
{
  // / (v.z - T(5))
  // / (v.z - T(5))
  return viewport_to_canvas<T>((v.x * T(0.5) + T(2.0/3.0)),
			       (v.y * T(0.5) + T(0.5)));
}

constexpr inline uint16_t rgb15(int32_t r, int32_t g, int32_t b)
{
  return ((b & 31) << 10) | ((g & 31) << 5) | ((r & 31) << 0);
}

constexpr uint16_t colors[] = {
  rgb15(31,  0,  0), // red
  rgb15( 0, 31,  0), // green
  rgb15( 0,  0, 31), // blue
  rgb15(31,  0, 31), // magenta
  rgb15( 0, 31, 31), // cyan
  rgb15(31, 31,  0), // yellow
};

static int32_t tick = 0;

void
render()
{
  tick++;
  int ix = 2;

  const int rx = tick >> 2;
  const mat3x3 rotationX {
    1,        0,       0,
    0,  cos(rx), sin(rx),
    0, -sin(rx), cos(rx)
  };

  const int ry = tick >> 1;
  const mat3x3 rotationY {
    cos(ry), 0, -sin(ry),
          0, 1,        0,
    sin(ry), 0,  cos(ry)
  };

  const mat3x3 transform = rotationX * rotationY;

  for (int i = 0; i < 6; i++) {

    const uint32_t * face = faces[i];

    // rotation
    const vec3& origin0 = transform * vertices[face[0]];
    // translation
    const vec3& origin{origin0.x, origin0.y + fp16_16(1), origin0.z + fp16_16(2)};

    const vec3& normal = transform * normals[i];
    const vec3 camera = {0, 0, 0};
    fp16_16 cull = dot((camera - origin), normal);

    if (cull.value > 0) {
      vdp1.vram.cmd[ix].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__POLYGON;
      vdp1.vram.cmd[ix].LINK = 0;
      vdp1.vram.cmd[ix].PMOD = PMOD__ECD | PMOD__SPD;
      vdp1.vram.cmd[ix].COLR = COLR__RGB | colors[i];

      // `origin` above is p==0 below; the `origin` calculation could
      // be reused, though it would hurt readability slightly
      for (int p = 0; p < 4; p++) {
	const vec3& v0 = vertices[face[p]];

	// rotation
	const vec3 v1 = transform * v0;
	// translation
	const vec3 v2{v1.x, v1.y + fp16_16(1), v1.z + fp16_16(2)};

	const vec3 v3 = project_vertex(v2 / v2.z);

	vdp1.vram.cmd[ix].point[p].X = static_cast<int>(v3.x);
	vdp1.vram.cmd[ix].point[p].Y = static_cast<int>(v3.y);
      }

      ix++;
    }
  }

  vdp1.vram.cmd[ix].CTRL = CTRL__END;
}

void main()
{
  v_blank_in();

  // DISP: Please make sure to change this bit from 0 to 1 during V blank.
  vdp2.reg.TVMD = ( TVMD__DISP | TVMD__LSMD__NON_INTERLACE
                  | TVMD__VRESO__240 | TVMD__HRESO__NORMAL_320);

  // disable all VDP2 backgrounds (e.g: the Sega bios logo)
  vdp2.reg.BGON = 0;

  // VDP2 User's Manual:
  // "When sprite data is in an RGB format, sprite register 0 is selected"
  // "When the value of a priority number is 0h, it is read as transparent"
  //
  // The power-on value of PRISA is zero. Set the priority for sprite register 0
  // to some number greater than zero, so that the color data is not interpreted
  // as "transparent".
  vdp2.reg.PRISA = PRISA__S0PRIN(1); // Sprite register 0 Priority Number

  /* TVM settings must be performed from the second H-blank IN interrupt after the
  V-blank IN interrupt to the H-blank IN interrupt immediately after the V-blank
  OUT interrupt. */
  // "normal" display resolution, 16 bits per pixel, 512x256 framebuffer
  vdp1.reg.TVMR = TVMR__TVM__NORMAL;

  // swap framebuffers every 1 cycle; non-interlace
  vdp1.reg.FBCR = 0;

  // during a framebuffer erase cycle, write the color "black" to each pixel
  constexpr uint16_t black = 0x0000;
  vdp1.reg.EWDR = black;

  // the EWLR/EWRR macros use somewhat nontrivial math for the X coordinates
  // erase upper-left coordinate
  vdp1.reg.EWLR = EWLR__16BPP_X1(0) | EWLR__Y1(0);

  // erase lower-right coordinate
  vdp1.reg.EWRR = EWRR__16BPP_X3(319) | EWRR__Y3(239);

  vdp1.vram.cmd[0].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__SYSTEM_CLIP_COORDINATES;
  vdp1.vram.cmd[0].LINK = 0;
  vdp1.vram.cmd[0].XC = 319;
  vdp1.vram.cmd[0].YC = 239;

  vdp1.vram.cmd[1].CTRL = CTRL__JP__JUMP_NEXT | CTRL__COMM__LOCAL_COORDINATE;
  vdp1.vram.cmd[1].LINK = 0;
  vdp1.vram.cmd[1].XA = 0;
  vdp1.vram.cmd[1].YA = 0;

  vdp1.vram.cmd[2].CTRL = CTRL__END;

  // start drawing (execute the command list) on every frame
  vdp1.reg.PTMR = PTMR__PTM__FRAME_CHANGE;

  while (true) {
    v_blank_in();
    render();
  }
}