diff --git a/include/NE2D.h b/include/NE2D.h
index 68c6ad7..0fc8b96 100644
--- a/include/NE2D.h
+++ b/include/NE2D.h
@@ -140,7 +140,7 @@ void NE_SpriteSystemEnd(void);
 /// function.
 ///
 /// @param sprite Sprite to be drawn.
-void NE_SpriteDraw(NE_Sprite *sprite);
+void NE_SpriteDraw(const NE_Sprite *sprite);
 
 /// Draws all visible sprites.
 ///
@@ -241,7 +241,7 @@ void NE_2DDrawQuadGradient(s16 x1, s16 y1, s16 x2, s16 y2, s16 z, u32 color1,
 /// @param z Priority.
 /// @param mat Material to use.
 void NE_2DDrawTexturedQuad(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                           NE_Material *mat);
+                           const NE_Material *mat);
 
 /// Draws a quad with a material at the given coordinates with a flat color.
 ///
@@ -253,7 +253,7 @@ void NE_2DDrawTexturedQuad(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
 /// @param mat Material to use.
 /// @param color Color
 void NE_2DDrawTexturedQuadColor(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                                NE_Material *mat, u32 color);
+                                const NE_Material *mat, u32 color);
 
 /// Draws a quad with a material at the given coordinates with a color gradient.
 ///
@@ -268,8 +268,8 @@ void NE_2DDrawTexturedQuadColor(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
 /// @param color3 Lower right color.
 /// @param color4 Lower left color.
 void NE_2DDrawTexturedQuadGradient(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                                   NE_Material *mat, u32 color1, u32 color2,
-                                   u32 color3, u32 color4);
+                                   const NE_Material *mat, u32 color1,
+                                   u32 color2, u32 color3, u32 color4);
 
 /// @}
 
diff --git a/include/NEGUI.h b/include/NEGUI.h
index 7ed2f39..69626f9 100644
--- a/include/NEGUI.h
+++ b/include/NEGUI.h
@@ -186,25 +186,25 @@ void NE_GUISlideBarSetMinMax(NE_GUIObj *sldbr, int min, int max);
 ///
 /// @param obj Pointer to the object.
 /// @return Event.
-NE_GUIState NE_GUIObjectGetEvent(NE_GUIObj *obj);
+NE_GUIState NE_GUIObjectGetEvent(const NE_GUIObj *obj);
 
 /// Gets the value of a check box.
 ///
 /// @param chbx Check box.
 /// @return It returns true if the check box is checked.
-bool NE_GUICheckBoxGetValue(NE_GUIObj *chbx);
+bool NE_GUICheckBoxGetValue(const NE_GUIObj *chbx);
 
 /// Gets the value of a radio button.
 ///
 /// @param rdbtn Radio button.
 /// @return It returns true if the radio button is checked.
-bool NE_GUIRadioButtonGetValue(NE_GUIObj *rdbtn);
+bool NE_GUIRadioButtonGetValue(const NE_GUIObj *rdbtn);
 
 /// Gets the value of a slide bar.
 ///
 /// @param sldbr Slide bar.
 /// @return It returns the value of the slide bar.
-int NE_GUISlideBarGetValue(NE_GUIObj *sldbr);
+int NE_GUISlideBarGetValue(const NE_GUIObj *sldbr);
 
 /// Deletes the given object.
 ///
diff --git a/include/NEModel.h b/include/NEModel.h
index 40a81a7..28e33f1 100644
--- a/include/NEModel.h
+++ b/include/NEModel.h
@@ -121,7 +121,7 @@ void NE_ModelSetAnimationSecondary(NE_Model *model, NE_Animation *anim);
 /// Draw a model.
 ///
 /// @param model Pointer to the model.
-void NE_ModelDraw(NE_Model *model);
+void NE_ModelDraw(const NE_Model *model);
 
 /// Clone model.
 ///
@@ -255,13 +255,13 @@ void NE_ModelAnimSecondarySetSpeed(NE_Model *model, int32_t speed);
 ///
 /// @param model Pointer to the model.
 /// @return Returns the frame in f32 format.
-int32_t NE_ModelAnimGetFrame(NE_Model *model);
+int32_t NE_ModelAnimGetFrame(const NE_Model *model);
 
 /// Returns the current frame of the secondary animation of an animated model.
 ///
 /// @param model Pointer to the model.
 /// @return Returns the frame in f32 format.
-int32_t NE_ModelAnimSecondaryGetFrame(NE_Model *model);
+int32_t NE_ModelAnimSecondaryGetFrame(const NE_Model *model);
 
 /// Sets the current frame of an animated model.
 ///
diff --git a/include/NEPalette.h b/include/NEPalette.h
index c2fef87..8d29c76 100644
--- a/include/NEPalette.h
+++ b/include/NEPalette.h
@@ -55,7 +55,7 @@ void NE_PaletteDelete(NE_Palette *pal);
 /// Tells the GPU to use the palette in the specified object.
 ///
 /// @param pal Pointer to the palette object.
-void NE_PaletteUse(NE_Palette *pal);
+void NE_PaletteUse(const NE_Palette *pal);
 
 /// Resets the palette system and sets the new max number of palettes.
 ///
@@ -96,7 +96,7 @@ void NE_PaletteSystemEnd(void);
 ///
 /// @param pal Palette to modify.
 /// @return Returns a pointer to the base address of the palette in VRAM.
-void *NE_PaletteModificationStart(NE_Palette *pal);
+void *NE_PaletteModificationStart(const NE_Palette *pal);
 
 /// Set the desired entry of a palette to a new color.
 ///
diff --git a/include/NEPhysics.h b/include/NEPhysics.h
index 501fff0..ac834dd 100644
--- a/include/NEPhysics.h
+++ b/include/NEPhysics.h
@@ -210,7 +210,7 @@ void NE_PhysicsOnCollision(NE_Physics *physics, NE_OnCollision action);
 ///
 /// @param pointer Pointer to the object.
 /// @return True if there is a collision, false otherwise.
-bool NE_PhysicsIsColliding(NE_Physics *pointer);
+bool NE_PhysicsIsColliding(const NE_Physics *pointer);
 
 /// Updates all physics objects.
 void NE_PhysicsUpdateAll(void);
@@ -228,7 +228,8 @@ void NE_PhysicsUpdate(NE_Physics *pointer);
 /// @param pointer1 Pointer to first object.
 /// @param pointer2 Pointer to second object.
 /// @return Returns true if two objects are colliding.
-bool NE_PhysicsCheckCollision(NE_Physics *pointer1, NE_Physics *pointer2);
+bool NE_PhysicsCheckCollision(const NE_Physics *pointer1,
+                              const NE_Physics *pointer2);
 
 /// @}
 
diff --git a/include/NEText.h b/include/NEText.h
index fec0c82..b0006ae 100644
--- a/include/NEText.h
+++ b/include/NEText.h
@@ -37,7 +37,7 @@ void NE_TextPriorityReset(void);
 /// @param mat Font texture.
 /// @param sizex (sizex, sizey) Size of one character.
 /// @param sizey (sizex, sizey) Size of one character.
-void NE_TextInit(int slot, NE_Material *mat, int sizex, int sizey);
+void NE_TextInit(int slot, const NE_Material *mat, int sizex, int sizey);
 
 /// Clears the given text font slot.
 ///
diff --git a/include/NETexture.h b/include/NETexture.h
index e39499e..c8bbeb4 100644
--- a/include/NETexture.h
+++ b/include/NETexture.h
@@ -136,7 +136,6 @@ void NE_MaterialTexClone(NE_Material *source, NE_Material *dest);
 /// @param pal Palette.
 void NE_MaterialTexSetPal(NE_Material *tex, NE_Palette *pal);
 
-
 /// Set active material to use when drawing polygons.
 ///
 /// If the pointer passed is NULL the function will disable textures and new
@@ -144,7 +143,7 @@ void NE_MaterialTexSetPal(NE_Material *tex, NE_Palette *pal);
 /// a valid material.
 ///
 /// @param tex Material to be used.
-void NE_MaterialUse(NE_Material *tex);
+void NE_MaterialUse(const NE_Material *tex);
 
 /// Flags to choose which VRAM banks Nitro Engine can use to allocate textures.
 typedef enum {
@@ -216,7 +215,7 @@ void NE_TextureSystemEnd(void);
 ///
 /// @param tex Material.
 /// @return Returns the size in pixels.
-int NE_TextureGetSizeX(NE_Material *tex);
+int NE_TextureGetSizeX(const NE_Material *tex);
 
 /// Returns the height of a texture.
 ///
@@ -224,7 +223,7 @@ int NE_TextureGetSizeX(NE_Material *tex);
 ///
 /// @param tex Material.
 /// @return Returns the size in pixels.
-int NE_TextureGetSizeY(NE_Material *tex);
+int NE_TextureGetSizeY(const NE_Material *tex);
 
 /// Returns the real width of a texture.
 ///
@@ -233,7 +232,7 @@ int NE_TextureGetSizeY(NE_Material *tex);
 ///
 /// @param tex Material.
 /// @return Returns the size in pixels.
-int NE_TextureGetRealSizeX(NE_Material *tex);
+int NE_TextureGetRealSizeX(const NE_Material *tex);
 
 /// Returns the real height size of a texture.
 ///
@@ -242,7 +241,7 @@ int NE_TextureGetRealSizeX(NE_Material *tex);
 ///
 /// @param tex Material.
 /// @return Returns the size in pixels.
-int NE_TextureGetRealSizeY(NE_Material *tex);
+int NE_TextureGetRealSizeY(const NE_Material *tex);
 
 /// Sets lighting propierties of this material.
 ///
@@ -282,7 +281,7 @@ void NE_MaterialSetDefaultPropierties(u32 diffuse, u32 ambient, u32 specular,
 ///
 /// @param tex Texture to modify.
 /// @return Returns a pointer to the base address of the texture in VRAM.
-void *NE_TextureDrawingStart(NE_Material *tex);
+void *NE_TextureDrawingStart(const NE_Material *tex);
 
 /// Sets the specified pixel to the specified color.
 ///
diff --git a/source/NE2D.c b/source/NE2D.c
index 047fc03..bdc1133 100644
--- a/source/NE2D.c
+++ b/source/NE2D.c
@@ -161,7 +161,7 @@ void NE_SpriteSystemEnd(void)
     ne_sprite_system_inited = false;
 }
 
-void NE_SpriteDraw(NE_Sprite *sprite)
+void NE_SpriteDraw(const NE_Sprite *sprite)
 {
     if (!ne_sprite_system_inited)
         return;
@@ -251,8 +251,8 @@ void NE_SpriteDrawAll(void)
 
 // Internal use. See NETexture.c
 
-int __NE_TextureGetRawX(NE_Material *tex);
-int __NE_TextureGetRawY(NE_Material *tex);
+int __NE_TextureGetRawX(const NE_Material *tex);
+int __NE_TextureGetRawY(const NE_Material *tex);
 
 //--------------------------------------------
 
@@ -355,7 +355,7 @@ void NE_2DDrawQuadGradient(s16 x1, s16 y1, s16 x2, s16 y2, s16 z, u32 color1,
 }
 
 void NE_2DDrawTexturedQuad(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                           NE_Material *mat)
+                           const NE_Material *mat)
 {
     NE_AssertPointer(mat, "NULL pointer");
     NE_Assert(mat->texindex != NE_NO_TEXTURE, "No texture");
@@ -382,7 +382,7 @@ void NE_2DDrawTexturedQuad(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
 }
 
 void NE_2DDrawTexturedQuadColor(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                                NE_Material *mat, u32 color)
+                                const NE_Material *mat, u32 color)
 {
     NE_AssertPointer(mat, "NULL pointer");
     NE_Assert(mat->texindex != NE_NO_TEXTURE, "No texture");
@@ -411,8 +411,8 @@ void NE_2DDrawTexturedQuadColor(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
 }
 
 void NE_2DDrawTexturedQuadGradient(s16 x1, s16 y1, s16 x2, s16 y2, s16 z,
-                                   NE_Material *mat, u32 color1, u32 color2,
-                                   u32 color3, u32 color4)
+                                   const NE_Material *mat, u32 color1,
+                                   u32 color2, u32 color3, u32 color4)
 {
     NE_AssertPointer(mat, "NULL pointer");
     NE_Assert(mat->texindex != NE_NO_TEXTURE, "No texture");
diff --git a/source/NEGUI.c b/source/NEGUI.c
index 1778ce8..b306d2a 100644
--- a/source/NEGUI.c
+++ b/source/NEGUI.c
@@ -912,7 +912,7 @@ void NE_GUISlideBarSetMinMax(NE_GUIObj *sldbr, int min, int max)
         slidebar->x1 + (slidebar->y2 - slidebar->y1);
 }
 
-NE_GUIState NE_GUIObjectGetEvent(NE_GUIObj *obj)
+NE_GUIState NE_GUIObjectGetEvent(const NE_GUIObj *obj)
 {
     ne_slidebar_t *ptr;
 
@@ -935,21 +935,21 @@ NE_GUIState NE_GUIObjectGetEvent(NE_GUIObj *obj)
     }
 }
 
-bool NE_GUICheckBoxGetValue(NE_GUIObj *chbx)
+bool NE_GUICheckBoxGetValue(const NE_GUIObj *chbx)
 {
     NE_AssertPointer(chbx, "NULL pointer");
     NE_Assert(chbx->type == NE_CheckBox, "Not a check box");
     return ((ne_checkbox_t *)(chbx->pointer))->checked;
 }
 
-bool NE_GUIRadioButtonGetValue(NE_GUIObj *rdbtn)
+bool NE_GUIRadioButtonGetValue(const NE_GUIObj *rdbtn)
 {
     NE_AssertPointer(rdbtn, "NULL pointer");
     NE_Assert(rdbtn->type == NE_RadioButton, "Not a radio button");
     return ((ne_radiobutton_t *)(rdbtn->pointer))->checked;
 }
 
-int NE_GUISlideBarGetValue(NE_GUIObj *sldbr)
+int NE_GUISlideBarGetValue(const NE_GUIObj *sldbr)
 {
     NE_AssertPointer(sldbr, "NULL pointer");
     NE_Assert(sldbr->type == NE_SlideBar, "Not a slide bar");
diff --git a/source/NEModel.c b/source/NEModel.c
index 2feb44d..ae39d77 100644
--- a/source/NEModel.c
+++ b/source/NEModel.c
@@ -176,7 +176,7 @@ void NE_ModelSetAnimationSecondary(NE_Model *model, NE_Animation *anim)
 // Internal use... see below
 extern bool NE_TestTouch;
 
-void NE_ModelDraw(NE_Model *model)
+void NE_ModelDraw(const NE_Model *model)
 {
     NE_AssertPointer(model, "NULL pointer");
     if (model->meshdata == NULL)
@@ -387,14 +387,14 @@ void NE_ModelAnimSecondarySetSpeed(NE_Model *model, int32_t speed)
     model->animinfo[1]->speed = speed;
 }
 
-int32_t NE_ModelAnimGetFrame(NE_Model *model)
+int32_t NE_ModelAnimGetFrame(const NE_Model *model)
 {
     NE_AssertPointer(model, "NULL pointer");
     NE_Assert(model->modeltype == NE_Animated, "Not an animated model");
     return model->animinfo[0]->currframe;
 }
 
-int32_t NE_ModelAnimSecondaryGetFrame(NE_Model *model)
+int32_t NE_ModelAnimSecondaryGetFrame(const NE_Model *model)
 {
     NE_AssertPointer(model, "NULL pointer");
     NE_Assert(model->modeltype == NE_Animated, "Not an animated model");
diff --git a/source/NEPalette.c b/source/NEPalette.c
index 2761502..129d2bb 100644
--- a/source/NEPalette.c
+++ b/source/NEPalette.c
@@ -145,7 +145,7 @@ void NE_PaletteDelete(NE_Palette *pal)
     NE_DebugPrint("Material not found");
 }
 
-void NE_PaletteUse(NE_Palette *pal)
+void NE_PaletteUse(const NE_Palette *pal)
 {
     NE_AssertPointer(pal, "NULL pointer");
     NE_Assert(pal->index != NE_NO_PALETTE, "No asigned palette");
@@ -262,7 +262,7 @@ void NE_PaletteSystemEnd(void)
 static u16 *palette_adress = NULL;
 static int palette_format;
 
-void *NE_PaletteModificationStart(NE_Palette *pal)
+void *NE_PaletteModificationStart(const NE_Palette *pal)
 {
     NE_AssertPointer(pal, "NULL pointer");
     NE_Assert(pal->index != NE_NO_PALETTE, "No asigned palette");
diff --git a/source/NEPhysics.c b/source/NEPhysics.c
index eaba598..d378064 100644
--- a/source/NEPhysics.c
+++ b/source/NEPhysics.c
@@ -191,7 +191,7 @@ void NE_PhysicsOnCollision(NE_Physics *physics, NE_OnCollision action)
     physics->oncollision = action;
 }
 
-bool NE_PhysicsIsColliding(NE_Physics *pointer)
+bool NE_PhysicsIsColliding(const NE_Physics *pointer)
 {
     NE_AssertPointer(pointer, "NULL pointer");
     return pointer->iscolliding;
@@ -405,7 +405,8 @@ void NE_PhysicsUpdate(NE_Physics *pointer)
     }
 }
 
-bool NE_PhysicsCheckCollision(NE_Physics *pointer1, NE_Physics *pointer2)
+bool NE_PhysicsCheckCollision(const NE_Physics *pointer1,
+                              const NE_Physics *pointer2)
 {
     NE_AssertPointer(pointer1, "NULL pointer 1");
     NE_AssertPointer(pointer2, "NULL pointer 2");
diff --git a/source/NEText.c b/source/NEText.c
index 8c4fa5c..2f152eb 100644
--- a/source/NEText.c
+++ b/source/NEText.c
@@ -10,7 +10,7 @@
 
 typedef struct {
     int sizex, sizey;
-    NE_Material *material;
+    const NE_Material *material;
 } ne_textinfo_t;
 
 static ne_textinfo_t NE_TextInfo[NE_MAX_TEXT_FONTS];
@@ -27,7 +27,7 @@ void NE_TextPriorityReset(void)
     NE_TEXT_PRIORITY = 0;
 }
 
-void NE_TextInit(int slot, NE_Material *mat, int sizex, int sizey)
+void NE_TextInit(int slot, const NE_Material *mat, int sizex, int sizey)
 {
     NE_AssertMinMax(0, slot, NE_MAX_TEXT_FONTS, "Invalid slot %d", slot);
     NE_AssertPointer(mat, "NULL pointer");
@@ -73,7 +73,7 @@ static void _ne_texturecuadprint(int xcrd1, int ycrd1, int xcrd2, int ycrd2,
     GFX_VERTEX_XY = (ycrd1 << 16) | (xcrd2 & 0xFFFF);
 }
 
-static void _ne_charprint(ne_textinfo_t * textinfo, int xcrd1, int ycrd1,
+static void _ne_charprint(const ne_textinfo_t * textinfo, int xcrd1, int ycrd1,
                           char character)
 {
     // Texture coords
@@ -92,7 +92,7 @@ int NE_TextPrint(int slot, int x, int y, u32 color, const char *text)
 {
     NE_AssertMinMax(0, slot, NE_MAX_TEXT_FONTS, "Invalid slot %d", slot);
 
-    ne_textinfo_t *textinfo = &NE_TextInfo[slot];
+    const ne_textinfo_t *textinfo = &NE_TextInfo[slot];
 
     if (textinfo->material == NULL)
         return -1;
@@ -142,7 +142,7 @@ int NE_TextPrintBox(int slot, int x, int y, int endx, int endy, u32 color,
 {
     NE_AssertMinMax(0, slot, NE_MAX_TEXT_FONTS, "Invalid slot %d", slot);
 
-    ne_textinfo_t *textinfo = &NE_TextInfo[slot];
+    const ne_textinfo_t *textinfo = &NE_TextInfo[slot];
 
     if (textinfo->material == NULL)
         return -1;
@@ -199,7 +199,7 @@ int NE_TextPrintFree(int slot, int x, int y, u32 color, const char *text)
 {
     NE_AssertMinMax(0, slot, NE_MAX_TEXT_FONTS, "Invalid slot %d", slot);
 
-    ne_textinfo_t *textinfo = &NE_TextInfo[slot];
+    const ne_textinfo_t *textinfo = &NE_TextInfo[slot];
 
     if (textinfo->material == NULL)
         return -1;
diff --git a/source/NETexture.c b/source/NETexture.c
index 280c814..7dc3939 100644
--- a/source/NETexture.c
+++ b/source/NETexture.c
@@ -417,7 +417,7 @@ void NE_MaterialTexSetPal(NE_Material *tex, NE_Palette *pal)
     NE_Texture[tex->texindex].palette = pal;
 }
 
-void NE_MaterialUse(NE_Material *tex)
+void NE_MaterialUse(const NE_Material *tex)
 {
     if (tex == NULL)
     {
@@ -653,7 +653,7 @@ void NE_TextureSystemEnd(void)
 }
 
 // Internal use
-int __NE_TextureGetRawX(NE_Material *tex)
+int __NE_TextureGetRawX(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE,
@@ -662,35 +662,35 @@ int __NE_TextureGetRawX(NE_Material *tex)
 }
 
 // Internal use
-int __NE_TextureGetRawY(NE_Material *tex)
+int __NE_TextureGetRawY(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");
     return (NE_Texture[tex->texindex].param & (0x7 << 23)) >> 23;
 }
 
-int NE_TextureGetRealSizeX(NE_Material *tex)
+int NE_TextureGetRealSizeX(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");
     return 8 << __NE_TextureGetRawX(tex);
 }
 
-int NE_TextureGetRealSizeY(NE_Material *tex)
+int NE_TextureGetRealSizeY(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");
     return 8 << __NE_TextureGetRawY(tex);
 }
 
-int NE_TextureGetSizeX(NE_Material *tex)
+int NE_TextureGetSizeX(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");
     return NE_Texture[tex->texindex].sizex;
 }
 
-int NE_TextureGetSizeY(NE_Material *tex)
+int NE_TextureGetSizeY(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");
@@ -732,7 +732,7 @@ static int drawingtexture_type;
 static int drawingtexture_realx;
 static u32 ne_vram_saved;
 
-void *NE_TextureDrawingStart(NE_Material *tex)
+void *NE_TextureDrawingStart(const NE_Material *tex)
 {
     NE_AssertPointer(tex, "NULL pointer");
     NE_Assert(tex->texindex != NE_NO_TEXTURE, "No texture asigned to material");