ogc: do not implement clearing by copying the EFB

While copying the EFB is probably more efficient, it causes screen
flashes (very noticeable on the console, and more rarely in Dolphin) due
to the fact that we might be writing to the XFB while it's been read by
the VI interface.

So, let's implement clearing by drawing a rectangle over the window;
this requires a little more code, but completely eliminates flashes.

Author: mardy

src/render/ogc/SDL_render_ogc.c

@@ -40,7 +40,6 @@
 typedef struct
 {
     SDL_BlendMode current_blend_mode;
-    GXColor clear_color;
     int ops_after_present;
     bool vsync;
     u8 efb_pixel_format;
@@ -459,16 +458,35 @@ static int OGC_RenderClear(SDL_Renderer *renderer, SDL_RenderCommand *cmd)
         cmd->data.color.b,
         cmd->data.color.a
     };
+    int16_t x1 = 0;
+    int16_t y1 = 0;
+    int16_t x2 = renderer->window->w;
+    int16_t y2 = renderer->window->h;
+    OGC_set_viewport(0, 0, renderer->window->w, renderer->window->h);
+    OGC_SetBlendMode(renderer, SDL_BLENDMODE_NONE);
 
-    data->clear_color = c;
-    GX_SetCopyClear(c, GX_MAX_Z24);
-    if (renderer->target) {
-        save_efb_to_texture(renderer->target, true);
-    } else {
-        GX_CopyDisp(OGC_video_get_xfb(SDL_GetVideoDevice()), GX_TRUE);
-    }
+    GX_ClearVtxDesc();
+    GX_SetVtxDesc(GX_VA_POS, GX_DIRECT);
+    GX_SetVtxAttrFmt(GX_VTXFMT0, GX_VA_POS, GX_POS_XY, GX_S16, 0);
+    GX_SetTevColor(GX_TEVREG0, c);
+    GX_SetTevColorIn(GX_TEVSTAGE0, GX_CC_C0, GX_CC_ZERO, GX_CC_ZERO, GX_CC_ZERO);
+    GX_SetTevAlphaIn(GX_TEVSTAGE0, GX_CA_A0, GX_CA_ZERO, GX_CA_ZERO, GX_CA_ZERO);
+    GX_SetTevColorOp(GX_TEVSTAGE0, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, GX_TEVPREV);
+    GX_SetTevAlphaOp(GX_TEVSTAGE0, GX_TEV_ADD, GX_TB_ZERO, GX_CS_SCALE_1, GX_TRUE, GX_TEVPREV);
+    GX_SetNumTevStages(1);
+    GX_SetNumChans(0);
+
+    GX_Begin(GX_QUADS, GX_VTXFMT0, 4);
+    GX_Position2s16(x1, y1);
+    GX_Position2s16(x2, y1);
+    GX_Position2s16(x2, y2);
+    GX_Position2s16(x1, y2);
+    GX_End();
     data->ops_after_present++;
 
+    /* Restore the viewport */
+    OGC_set_viewport(renderer->viewport.x, renderer->viewport.y,
+                     renderer->viewport.w, renderer->viewport.h);
     return 0;
 }