Fixed bug 4542 - Image flipped vertically when rendering on texture

Have to recompute  viewport because projection/glOrtho is different
wether rendering is on target texture or not

src/render/opengl/SDL_render_gl.c

@@ -773,6 +773,8 @@ GL_SetRenderTarget(SDL_Renderer * renderer, SDL_Texture * texture)
         return SDL_SetError("Render targets not supported by OpenGL");
     }
 
+    data->drawstate.viewport_dirty = SDL_TRUE;
+
     if (texture == NULL) {
         data->glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
         return 0;
@@ -1525,7 +1527,7 @@ GL_CreateRenderer(SDL_Window * window, Uint32 flags)
     SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile_mask);
     SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major);
     SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor);
-    
+
     window_flags = SDL_GetWindowFlags(window);
     if (!(window_flags & SDL_WINDOW_OPENGL) ||
         profile_mask == SDL_GL_CONTEXT_PROFILE_ES || major != RENDERER_CONTEXT_MAJOR || minor != RENDERER_CONTEXT_MINOR) {

src/render/opengles/SDL_render_gles.c

@@ -503,6 +503,8 @@ GLES_SetRenderTarget(SDL_Renderer * renderer, SDL_Texture * texture)
         return SDL_SetError("Can't enable render target support in this renderer");
     }
 
+    data->drawstate.viewport_dirty = SDL_TRUE;
+
     if (texture == NULL) {
         data->glBindFramebufferOES(GL_FRAMEBUFFER_OES, data->window_framebuffer);
         return 0;

src/render/opengles2/SDL_render_gles2.c

@@ -1748,6 +1748,8 @@ GLES2_SetRenderTarget(SDL_Renderer * renderer, SDL_Texture * texture)
     GLES2_TextureData *texturedata = NULL;
     GLenum status;
 
+    data->drawstate.viewport_dirty = SDL_TRUE;
+
     if (texture == NULL) {
         data->glBindFramebuffer(GL_FRAMEBUFFER, data->window_framebuffer);
     } else {