[WIP] Transform SuperTux into a 3D game

src/supertux/gameconfig.cpp

@@ -67,6 +67,7 @@ Config::Config() :
   flash_intensity(50),
   max_viewport(false),
   fancy_gfx(true),
+  enable_3d_mode(false),
   precise_scrolling(true),
   invert_wheel_x(false),
   invert_wheel_y(false),
@@ -330,6 +331,7 @@ Config::load()
 
     config_video_mapping->get("magnification", magnification);
     config_video_mapping->get("fancy_gfx", fancy_gfx);
+    config_video_mapping->get("enable_3d_mode", enable_3d_mode);
     config_video_mapping->get("prefer_wayland", prefer_wayland);
     config_video_mapping->get("max_viewport", max_viewport);
 
@@ -511,6 +513,7 @@ Config::save()
 
   writer.write("magnification", magnification);
   writer.write("fancy_gfx", fancy_gfx);
+  writer.write("enable_3d_mode", enable_3d_mode);
   writer.write("prefer_wayland", prefer_wayland);
   writer.write("max_viewport", max_viewport);
 

src/supertux/gameconfig.hpp

@@ -90,6 +90,9 @@ class Config final
   /** Toggles fancy graphical effects like displacement or blur (primarily for the GL backend) */
   bool fancy_gfx;
 
+  /** Enable 3D perspective mode */
+  bool enable_3d_mode;
+
   /** initial random seed.  0 ==> set from time() */
   int random_seed;
 

src/supertux/menu/options_menu.cpp

@@ -127,6 +127,9 @@ OptionsMenu::refresh()
       add_toggle(MNID_FANCY_GFX, _("Fancy Effects"), &g_config->fancy_gfx)
         .set_help(_("Applies fancy effects such as blur, clear tile refraction, and various other effects deemed \"fancy\". May significantly degrade performance."));
 
+      add_toggle(MNID_3D_MODE, _("3D Mode"), &g_config->enable_3d_mode)
+        .set_help(_("Enables an isometric 3D perspective effect for the game."));
+
       add_flash_intensity();
 
 #if !defined(HIDE_NONMOBILE_OPTIONS) && !defined(__EMSCRIPTEN__)

src/supertux/menu/options_menu.hpp

@@ -68,6 +68,7 @@ class OptionsMenu final : public Menu
     MNID_VSYNC,
     MNID_FRAME_PREDICTION,
     MNID_FANCY_GFX,
+    MNID_3D_MODE,
     MNID_SOUND,
     MNID_MUSIC,
     MNID_SOUND_VOLUME,

src/video/gl/gl20_context.cpp

@@ -67,6 +67,22 @@ GL20Context::ortho(float width, float height, bool vflip)
 
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
+
+  // Apply 3D isometric-like perspective transformation when enabled
+  if (g_config && g_config->enable_3d_mode) {
+    // True isometric projection with 30-degree angles for dramatic 3D effect
+    const GLfloat cos30 = 0.866f;  // cos(30°)
+    const GLfloat sin30 = 0.5f;     // sin(30°)
+
+    // Isometric transformation matrix combining rotation and scaling
+    const GLfloat iso_matrix[] = {
+      cos30,  sin30,  0.0f, 0.0f,      // X axis rotated
+      -sin30, cos30 * 0.5f, 0.0f, 0.0f, // Y axis compressed and rotated
+      0.0f,   0.0f,   1.0f, 0.0f,
+      0.0f,   0.0f,   0.0f, 1.0f
+    };
+    glMultMatrixf(iso_matrix);
+  }
 
   assert_gl();
 }

src/video/gl/gl33core_context.cpp

@@ -125,11 +125,38 @@ GL33CoreContext::ortho(float width, float height, bool vflip)
   const float tx = -1.0f;
   const float ty = 1.0f * (vflip ? 1.0f : -1.0f);
 
-  const float mvp_matrix[] = {
-    sx, 0, tx,
-    0, sy, ty,
-    0, 0, 1
-  };
+  float mvp_matrix[9];
+
+  // Apply 3D isometric-like perspective transformation when enabled
+  if (g_config && g_config->enable_3d_mode) {
+    // True isometric projection with 30-degree angles
+    // This creates a dramatic 3D appearance by rotating the view
+    const float cos30 = 0.866f;  // cos(30°)
+    const float sin30 = 0.5f;     // sin(30°)
+
+    // Combine rotation and skew for isometric effect
+    // X stays the same, Y is compressed and offset by X
+    mvp_matrix[0] = sx * cos30;           // X scale with rotation
+    mvp_matrix[1] = sx * sin30;           // X contribution to Y
+    mvp_matrix[2] = tx;
+    mvp_matrix[3] = -sy * sin30;          // Y contribution to X (creates depth)
+    mvp_matrix[4] = sy * cos30 * 0.5f;    // Y scale (compressed for isometric)
+    mvp_matrix[5] = ty;
+    mvp_matrix[6] = 0;
+    mvp_matrix[7] = 0;
+    mvp_matrix[8] = 1;
+  } else {
+    // Standard orthographic projection
+    mvp_matrix[0] = sx;
+    mvp_matrix[1] = 0;
+    mvp_matrix[2] = tx;
+    mvp_matrix[3] = 0;
+    mvp_matrix[4] = sy;
+    mvp_matrix[5] = ty;
+    mvp_matrix[6] = 0;
+    mvp_matrix[7] = 0;
+    mvp_matrix[8] = 1;
+  }
 
   const GLint mvp_loc = m_program->get_modelviewprojection_location();
   glUniformMatrix3fv(mvp_loc, 1, false, mvp_matrix);