direct3d: Commit viewport state before clearing, attempt 2.

This reintroduces the fix from 0e16ee8330606603, but just marks
the viewport state as dirty after a clear that needs to expand the
viewport to fill the render target, as we'll need to also reset
the orthographic projection state elsewhere, and that won't
happen if we clear the dirty flag here.

Fixes #4210.
(again.)
(...sorry...!)

src/render/direct3d/SDL_render_d3d.c

@@ -1318,6 +1318,7 @@ D3D_RunCommandQueue(SDL_Renderer * renderer, SDL_RenderCommand *cmd, void *verti
                 const SDL_Rect *viewport = &data->drawstate.viewport;
                 const int backw = istarget ? renderer->target->w : data->pparams.BackBufferWidth;
                 const int backh = istarget ? renderer->target->h : data->pparams.BackBufferHeight;
+                const SDL_bool viewport_equal = ((viewport->x == 0) && (viewport->y == 0) && (viewport->w == backw) && (viewport->h == backh)) ? SDL_TRUE : SDL_FALSE;
 
                 if (data->drawstate.cliprect_enabled || data->drawstate.cliprect_enabled_dirty) {
                     IDirect3DDevice9_SetRenderState(data->device, D3DRS_SCISSORTESTENABLE, FALSE);
@@ -1325,13 +1326,13 @@ D3D_RunCommandQueue(SDL_Renderer * renderer, SDL_RenderCommand *cmd, void *verti
                 }
 
                 /* Don't reset the viewport if we don't have to! */
-                if (!viewport->x && !viewport->y && (viewport->w == backw) && (viewport->h == backh)) {
+                if (!data->drawstate.viewport_dirty && viewport_equal) {
                     IDirect3DDevice9_Clear(data->device, 0, NULL, D3DCLEAR_TARGET, color, 0.0f, 0);
                 } else {
                     /* Clear is defined to clear the entire render target */
                     const D3DVIEWPORT9 wholeviewport = { 0, 0, backw, backh, 0.0f, 1.0f };
                     IDirect3DDevice9_SetViewport(data->device, &wholeviewport);
-                    data->drawstate.viewport_dirty = SDL_TRUE;
+                    data->drawstate.viewport_dirty = SDL_TRUE;  /* we still need to (re)set orthographic projection, so always mark it dirty. */
                     IDirect3DDevice9_Clear(data->device, 0, NULL, D3DCLEAR_TARGET, color, 0.0f, 0);
                 }