add rotating 3d cube

Reviewed-on: #32

include/dangerzone/engine.h

@@ -9,6 +9,10 @@ typedef enum {
     OVERDRAW
 } framebuffer_e;
 
+typedef struct {
+    double x, y;
+} v2;
+
 typedef struct {
 	SDL_Event event;
 	bool is_running;

include/dangerzone/render/misc.h

@@ -17,3 +17,20 @@ clear_framebuffer(
     framebuffer_e framebuffer,
 	uint32_t color
 );
+
+void
+put_line(
+    v2 a,
+    v2 b,
+    framebuffer_e framebuffer,
+    uint32_t color
+);
+
+void
+put_triangle(
+    v2 a,
+    v2 b,
+    v2 c,
+    framebuffer_e framebuffer,
+    uint32_t color
+);

src/engine/render/misc.c

@@ -6,6 +6,8 @@
 #include "internal/util/error.h"
 
 #include <stdint.h>
+#include <stdlib.h>
+#include <math.h>
 
 // helper function to return the correct pointer to a framebuffer for drawing selection
 uint32_t*
@@ -69,3 +71,84 @@ clear_framebuffer(
         game_state->height
     );
 }
+
+void
+normalize_v2(
+    v2 input,
+    v2 *output
+) {
+    double min = (input.x > input.y) ? input.y : input.x;
+
+    for (int i = min; i > 1; i--) {
+        if ((int)input.x % (int)min == 0 && (int)input.y % (int)min == 0) {
+            input.x /= min;
+            input.y /= min;
+
+            break;
+        }
+    }
+
+    output->x = input.x;
+    output->y = input.y;
+}
+
+// subtract vector b from vector a
+void
+sub_v2(
+    v2 a,
+    v2 b,
+    v2 *dest
+) {
+    dest->x = b.x - a.x;
+    dest->y = b.y - a.y;
+}
+
+// draw a line between two points with a given color
+void
+put_line(
+    v2 a, v2 b,
+    framebuffer_e fb,
+    uint32_t color
+) {
+    int x0 = (int)round(a.x);
+    int y0 = (int)round(a.y);
+    int x1 = (int)round(b.x);
+    int y1 = (int)round(b.y);
+
+    int dx = abs(x1 - x0);
+    int sx = x0 < x1 ? 1 : -1;
+    int dy = -abs(y1 - y0);
+    int sy = y0 < y1 ? 1 : -1;
+    int err = dx + dy;
+
+    while (1) {
+        put_pixel(fb, x0, y0, color);
+
+        if (x0 == x1 && y0 == y1)
+            break;
+
+        int e2 = 2 * err;
+        if (e2 >= dy) {
+            err += dy;
+            x0 += sx;
+        }
+        if (e2 <= dx) {
+            err += dx;
+            y0 += sy;
+        }
+    }
+}
+
+// draw a frame of a triangle with a given color
+void
+put_triangle(
+    v2 a,
+    v2 b,
+    v2 c,
+    framebuffer_e framebuffer,
+    uint32_t color
+) {
+    put_line(a, b, framebuffer, color);
+    put_line(b, c, framebuffer, color);
+    put_line(a, c, framebuffer, color);
+}

src/examples/3d.c

@@ -0,0 +1,231 @@
+#include <dangerzone/engine.h>
+#include <dangerzone/render/misc.h>
+
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// a point in 3D space
+typedef struct
+{
+    double x, y, z;
+} v3;
+
+// a triangle with 3 points in 3D space
+typedef struct
+{
+    v3 p[3];
+} tri;
+
+// a grouping of triangles - can desribe any 3D object
+typedef struct
+{
+    tri *tris;
+} mesh;
+
+typedef struct
+{
+    float m[4][4];
+} mat4x4;
+
+#define PI 3.1415926535
+
+void multiply_matrix_vector(v3 input, v3 *output, mat4x4 m)
+{
+    output->x = input.x * m.m[0][0] + input.y * m.m[1][0] + input.z * m.m[2][0] + m.m[3][0];
+    output->y = input.x * m.m[0][1] + input.y * m.m[1][1] + input.z * m.m[2][1] + m.m[3][1];
+    output->z = input.x * m.m[0][2] + input.y * m.m[1][2] + input.z * m.m[2][2] + m.m[3][2];
+    double w = input.x * m.m[0][3] + input.y * m.m[1][3] + input.z * m.m[2][3] + m.m[3][3];
+
+    if (w != 0)
+    {
+        output->x /= w;
+        output->y /= w;
+        output->z /= w;
+    }
+}
+
+#define ASSERT(_e) do { if (!(_e)) { fprintf(stderr, "assert failed for %s\n", #_e); exit(1); } } while (0)
+
+struct {
+    mesh m;
+    mat4x4 mproj;
+    double near, far, fov;
+    unsigned int screen_width, screen_height;
+} state;
+
+// a unit-sized cube mesh defined with triangles
+#define CUBE_TRI_AMOUNT 12
+
+tri cube_mesh[CUBE_TRI_AMOUNT] =
+{
+    // south
+    {{ {0,0,0}, {0,1,0}, {1,1,0} }},
+    {{ {0,0,0}, {1,1,0}, {1,0,0} }},
+    // west
+    {{ {1,0,0}, {1,1,0}, {1,1,1} }},
+    {{ {1,0,0}, {1,1,1}, {1,0,1} }},
+    // north
+    {{ {1,0,1}, {1,1,1}, {0,1,1} }},
+    {{ {1,0,1}, {0,1,1}, {0,0,1} }},
+    // east
+    {{ {0,0,1}, {0,1,1}, {0,1,0} }},
+    {{ {0,0,1}, {0,1,0}, {0,0,0} }},
+    // top
+    {{ {0,1,0}, {0,1,1}, {1,1,1} }},
+    {{ {0,1,0}, {1,1,1}, {1,1,0} }},
+    // bottom
+    {{ {0,0,1}, {0,0,0}, {1,0,0} }},
+    {{ {0,0,1}, {1,0,0}, {1,0,1} }},
+};
+
+void
+game_init()
+{
+    state.m.tris = cube_mesh;
+
+    memset(&state.mproj, 0, sizeof(state.mproj));
+
+    state.near = 0.1;
+    state.far = 1000000.0;
+    state.fov = 90.0;
+    state.screen_width = 500;
+    state.screen_height = 500;
+
+    // aspect ratio
+    double a = (float)state.screen_height / (float)state.screen_width;
+
+    // fov tangent
+    double fov_rad = 1.0 / tanf(state.fov * 0.5 / 180.0 * PI);
+
+    state.mproj.m[0][0] = a * fov_rad;
+    state.mproj.m[1][1] = fov_rad;
+    state.mproj.m[2][2] = state.far / (state.far - state.near);
+    state.mproj.m[3][2] = (-state.far * state.near) / (state.far - state.near);
+    state.mproj.m[2][3] = 1.0;
+}
+
+void
+client_poll_events()
+{
+    SDL_Event ev = game_state->event;
+
+    if (ev.type == SDL_EVENT_QUIT) {
+        game_state->is_running = false;
+    }
+
+    if (ev.type == SDL_EVENT_KEY_DOWN) {
+        switch (ev.key.key) {
+        case SDLK_Q:
+            game_state->is_running = false;
+            break;
+        default:
+            break;
+        }
+    }
+}
+
+
+void
+client_update_framebuffer()
+{
+    clear_framebuffer(BASE, 0x000000);
+    clear_framebuffer(OVERDRAW, 0x000000);
+
+    mat4x4 mrotz = { 0 }, mrotx = { 0 };
+
+    double theta = SDL_GetTicks() / 1000.0;
+
+    // Rotation Z
+    mrotz.m[0][0] = cosf(theta);
+    mrotz.m[0][1] = sinf(theta);
+    mrotz.m[1][0] = -sinf(theta);
+    mrotz.m[1][1] = cosf(theta);
+    mrotz.m[2][2] = 1;
+    mrotz.m[3][3] = 1;
+
+    // Rotation X
+    mrotx.m[0][0] = 1;
+    mrotx.m[1][1] = cosf(theta * 0.5f);
+    mrotx.m[1][2] = sinf(theta * 0.5f);
+    mrotx.m[2][1] = -sinf(theta * 0.5f);
+    mrotx.m[2][2] = cosf(theta * 0.5f);
+    mrotx.m[3][3] = 1;
+
+    for (int i = 0; i < CUBE_TRI_AMOUNT; i++)
+    {
+        // project from 3D to 2D
+        tri triangle = state.m.tris[i];
+        for (int k = 0; k < 3; k++) {
+            triangle.p[k].x -= 0.5;
+            triangle.p[k].y -= 0.5;
+            triangle.p[k].z -= 0.5;
+        }
+        tri projected, translated, rotatedz, rotatedzx;
+
+        multiply_matrix_vector(triangle.p[0], &rotatedz.p[0], mrotz);
+        multiply_matrix_vector(triangle.p[1], &rotatedz.p[1], mrotz);
+        multiply_matrix_vector(triangle.p[2], &rotatedz.p[2], mrotz);
+
+        multiply_matrix_vector(rotatedz.p[0], &rotatedzx.p[0], mrotx);
+        multiply_matrix_vector(rotatedz.p[1], &rotatedzx.p[1], mrotx);
+        multiply_matrix_vector(rotatedz.p[2], &rotatedzx.p[2], mrotx);
+
+        translated = rotatedzx;
+        translated.p[0].z = rotatedzx.p[0].z + 3.0;
+        translated.p[1].z = rotatedzx.p[1].z + 3.0;
+        translated.p[2].z = rotatedzx.p[2].z + 3.0;
+
+        multiply_matrix_vector(translated.p[0], &projected.p[0], state.mproj);
+        multiply_matrix_vector(translated.p[1], &projected.p[1], state.mproj);
+        multiply_matrix_vector(translated.p[2], &projected.p[2], state.mproj);
+
+        // scale into view
+        projected.p[0].x += 1.0;
+        projected.p[0].y += 1.0;
+
+        projected.p[1].x += 1.0;
+        projected.p[1].y += 1.0;
+
+        projected.p[2].x += 1.0;
+        projected.p[2].y += 1.0;
+
+
+        projected.p[0].x *= 0.5 * state.screen_width;
+        projected.p[0].y *= 0.5 * state.screen_height;
+
+        projected.p[1].x *= 0.5 * state.screen_width;
+        projected.p[1].y *= 0.5 * state.screen_height;
+
+        projected.p[2].x *= 0.5 * state.screen_width;
+        projected.p[2].y *= 0.5 * state.screen_height;
+
+
+        put_triangle(
+            (v2){.x=projected.p[0].x, .y=projected.p[0].y},
+            (v2){.x=projected.p[1].x, .y=projected.p[1].y},
+            (v2){.x=projected.p[2].x, .y=projected.p[2].y},
+            OVERDRAW, 0xFFFFFF
+        );
+    }
+}
+
+
+int main()
+{
+    game_init();
+
+    if (engine_init(
+        state.screen_width, state.screen_height, "3D demo",
+        client_poll_events, client_update_framebuffer
+    )) {
+        engine_start();
+
+        engine_stop();
+
+        return 0;
+    } else {
+        return 1;
+    }
+}

src/examples/CMakeLists.txt

@@ -5,5 +5,9 @@ add_executable(game_2048 2048.c)
 target_link_libraries(game_2048 PRIVATE dangerzone_engine)
 target_link_libraries(game_2048 PRIVATE m)
 
+add_executable(game_3d 3d.c)
+target_link_libraries(game_3d PRIVATE dangerzone_engine)
+target_link_libraries(game_3d PRIVATE m)
+
 #add_executable(game_window window.c)
 #target_link_libraries(game_window PRIVATE dangerzone_engine)