ogc: reset cull mode, Z-buffering and alpha compare when drawing cursor

OpenGX might have set the GPU to perform Z-buffering, triangle culling
and alpha compare in such a way that our mouse cursor will not be drawn.
For that reason, reset them to ensure that our cursor will always be
drawn.

Extra care must be put to restore these registers to the same state in
which SDL had set them before, in order not to break 2D applications.

src/video/ogc/SDL_ogcmouse.c

@@ -31,6 +31,7 @@
 #include "SDL_ogcpixels.h"
 
 #include "../SDL_sysvideo.h"
+#include "../../render/SDL_sysrender.h"
 
 #include <malloc.h>
 #include <ogc/cache.h>
@@ -203,6 +204,8 @@ void OGC_draw_cursor(_THIS)
     guMtxTransApply(mv, mv, mouse->x, mouse->y, 0);
     GX_LoadPosMtxImm(mv, GX_PNMTX1);
 
+    OGC_set_viewport(0, 0, screen_w, screen_h);
+
     GX_ClearVtxDesc();
     GX_SetVtxDesc(GX_VA_POS, GX_DIRECT);
     GX_SetVtxDesc(GX_VA_TEX0, GX_DIRECT);
@@ -214,12 +217,28 @@ void OGC_draw_cursor(_THIS)
     GX_SetTevOrder(GX_TEVSTAGE0, GX_TEXCOORD0, GX_TEXMAP0, GX_COLOR0A0);
     GX_SetNumTevStages(1);
     GX_SetBlendMode(GX_BM_BLEND, GX_BL_SRCALPHA, GX_BL_INVSRCALPHA, GX_LO_CLEAR);
+    GX_SetZMode(GX_DISABLE, GX_ALWAYS, GX_FALSE);
+    GX_SetCullMode(GX_CULL_NONE);
+    GX_SetAlphaCompare(GX_ALWAYS, 0, GX_AOP_AND, GX_ALWAYS, 0);
+
 
     GX_SetNumTexGens(1);
     GX_SetCurrentMtx(GX_PNMTX1);
     draw_cursor_rect(curdata);
     GX_SetCurrentMtx(GX_PNMTX0);
     GX_DrawDone();
+
+    /* Restore default state for SDL (opengx restores it at every frame, so we
+     * don't care about it) */
+    GX_SetZMode(GX_TRUE, GX_LEQUAL, GX_TRUE);
+    if (_this->windows) {
+        /* Restore previous viewport for the renderer */
+        SDL_Renderer *renderer = SDL_GetRenderer(_this->windows);
+        if (renderer) {
+            OGC_set_viewport(renderer->viewport.x, renderer->viewport.y,
+                             renderer->viewport.w, renderer->viewport.h);
+        }
+    }
 }
 
 #endif /* SDL_VIDEO_DRIVER_OGC */