render: allow render targets to use logical presentation.

Fixes libsdl-org/sdl2-compat#279

include/SDL3/SDL_render.h

@@ -490,6 +490,9 @@ extern SDL_DECLSPEC SDL_PropertiesID SDLCALL SDL_GetRendererProperties(SDL_Rende
  * This returns the true output size in pixels, ignoring any render targets or
  * logical size and presentation.
  *
+ * For the output size of the current rendering target, with logical size
+ * adjustments, use SDL_GetCurrentRenderOutputSize() instead.
+ *
  * \param renderer the rendering context.
  * \param w a pointer filled in with the width in pixels.
  * \param h a pointer filled in with the height in pixels.
@@ -508,9 +511,10 @@ extern SDL_DECLSPEC bool SDLCALL SDL_GetRenderOutputSize(SDL_Renderer *renderer,
  * Get the current output size in pixels of a rendering context.
  *
  * If a rendering target is active, this will return the size of the rendering
- * target in pixels, otherwise if a logical size is set, it will return the
- * logical size, otherwise it will return the value of
- * SDL_GetRenderOutputSize().
+ * target in pixels, otherwise return the value of SDL_GetRenderOutputSize().
+ *
+ * Rendering target or not, the output will be adjusted by the current
+ * logical presentation state, dictated by SDL_SetRenderLogicalPresentation().
  *
  * \param renderer the rendering context.
  * \param w a pointer filled in with the current width.
@@ -1318,6 +1322,11 @@ extern SDL_DECLSPEC void SDLCALL SDL_UnlockTexture(SDL_Texture *texture);
  * To stop rendering to a texture and render to the window again, call this
  * function with a NULL `texture`.
  *
+ * Viewport, cliprect, scale, and logical presentation are unique to each
+ * render target. Get and set functions for these states apply to the current
+ * render target set by this function, and those states persist on each target
+ * when the current render target changes.
+ *
  * \param renderer the rendering context.
  * \param texture the targeted texture, which must be created with the
  *                `SDL_TEXTUREACCESS_TARGET` flag, or NULL to render to the
@@ -1351,25 +1360,39 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderTarget(SDL_Renderer *renderer, SDL
 extern SDL_DECLSPEC SDL_Texture * SDLCALL SDL_GetRenderTarget(SDL_Renderer *renderer);
 
 /**
- * Set a device independent resolution and presentation mode for rendering.
+ * Set a device-independent resolution and presentation mode for rendering.
  *
  * This function sets the width and height of the logical rendering output.
- * The renderer will act as if the window is always the requested dimensions,
- * scaling to the actual window resolution as necessary.
+ * The renderer will act as if the current render target is always the
+ * requested dimensions, scaling to the actual resolution as necessary.
  *
  * This can be useful for games that expect a fixed size, but would like to
  * scale the output to whatever is available, regardless of how a user resizes
  * a window, or if the display is high DPI.
  *
+ * Logical presentation can be used with both render target textures
+ * and the renderer's window; the state is unique to each render target, and
+ * this function sets the state for the current render target. It might be
+ * useful to draw to a texture that matches the window dimensions with logical
+ * presentation enabled, and then draw that texture across the entire window
+ * with logical presentation disabled. Be careful not to render both with
+ * logical presentation enabled, however, as this could produce
+ * double-letterboxing, etc.
+ *
  * You can disable logical coordinates by setting the mode to
  * SDL_LOGICAL_PRESENTATION_DISABLED, and in that case you get the full pixel
- * resolution of the output window; it is safe to toggle logical presentation
+ * resolution of the render target; it is safe to toggle logical presentation
  * during the rendering of a frame: perhaps most of the rendering is done to
  * specific dimensions but to make fonts look sharp, the app turns off logical
- * presentation while drawing text.
+ * presentation while drawing text, for example.
  *
- * Letterboxing will only happen if logical presentation is enabled during
- * SDL_RenderPresent; be sure to reenable it first if you were using it.
+ * For the renderer's window, letterboxing is drawn into the framebuffer
+ * if logical presentation is enabled during SDL_RenderPresent; be sure to
+ * reenable it before presenting if you were toggling it, otherwise the
+ * letterbox areas might have artifacts from previous frames (or artifacts
+ * from external overlays, etc). Letterboxing is never drawn into texture
+ * render targets; be sure to call SDL_RenderClear() before drawing into
+ * the texture so the letterboxing areas are cleared, if appropriate.
  *
  * You can convert coordinates in an event into rendering coordinates using
  * SDL_ConvertEventToRenderCoordinates().
@@ -1397,6 +1420,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderLogicalPresentation(SDL_Renderer *
  * This function gets the width and height of the logical rendering output, or
  * the output size in pixels if a logical resolution is not enabled.
  *
+ * Each render target has its own logical presentation state. This function
+ * gets the state for the current render target.
+ *
  * \param renderer the rendering context.
  * \param w an int to be filled with the width.
  * \param h an int to be filled with the height.
@@ -1420,6 +1446,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_GetRenderLogicalPresentation(SDL_Renderer *
  * presentation is disabled, it will fill the rectangle with the output size,
  * in pixels.
  *
+ * Each render target has its own logical presentation state. This function
+ * gets the rectangle for the current render target.
+ *
  * \param renderer the rendering context.
  * \param rect a pointer filled in with the final presentation rectangle, may
  *             be NULL.
@@ -1536,6 +1565,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_ConvertEventToRenderCoordinates(SDL_Rendere
  *
  * The area's width and height must be >= 0.
  *
+ * Each render target has its own viewport. This function sets the viewport
+ * for the current render target.
+ *
  * \param renderer the rendering context.
  * \param rect the SDL_Rect structure representing the drawing area, or NULL
  *             to set the viewport to the entire target.
@@ -1554,6 +1586,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderViewport(SDL_Renderer *renderer, c
 /**
  * Get the drawing area for the current target.
  *
+ * Each render target has its own viewport. This function gets the viewport
+ * for the current render target.
+ *
  * \param renderer the rendering context.
  * \param rect an SDL_Rect structure filled in with the current drawing area.
  * \returns true on success or false on failure; call SDL_GetError() for more
@@ -1575,6 +1610,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_GetRenderViewport(SDL_Renderer *renderer, S
  * whether you should restore a specific rectangle or NULL. Note that the
  * viewport is always reset when changing rendering targets.
  *
+ * Each render target has its own viewport. This function checks the viewport
+ * for the current render target.
+ *
  * \param renderer the rendering context.
  * \returns true if the viewport was set to a specific rectangle, or false if
  *          it was set to NULL (the entire target).
@@ -1613,6 +1651,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_GetRenderSafeArea(SDL_Renderer *renderer, S
 /**
  * Set the clip rectangle for rendering on the specified target.
  *
+ * Each render target has its own clip rectangle. This function
+ * sets the cliprect for the current render target.
+ *
  * \param renderer the rendering context.
  * \param rect an SDL_Rect structure representing the clip area, relative to
  *             the viewport, or NULL to disable clipping.
@@ -1631,6 +1672,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderClipRect(SDL_Renderer *renderer, c
 /**
  * Get the clip rectangle for the current target.
  *
+ * Each render target has its own clip rectangle. This function
+ * gets the cliprect for the current render target.
+ *
  * \param renderer the rendering context.
  * \param rect an SDL_Rect structure filled in with the current clipping area
  *             or an empty rectangle if clipping is disabled.
@@ -1647,7 +1691,10 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderClipRect(SDL_Renderer *renderer, c
 extern SDL_DECLSPEC bool SDLCALL SDL_GetRenderClipRect(SDL_Renderer *renderer, SDL_Rect *rect);
 
 /**
- * Get whether clipping is enabled on the given renderer.
+ * Get whether clipping is enabled on the given render target.
+ *
+ * Each render target has its own clip rectangle. This function
+ * checks the cliprect for the current render target.
  *
  * \param renderer the rendering context.
  * \returns true if clipping is enabled or false if not; call SDL_GetError()
@@ -1673,6 +1720,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_RenderClipEnabled(SDL_Renderer *renderer);
  * will be handled using the appropriate quality hints. For best results use
  * integer scaling factors.
  *
+ * Each render target has its own scale. This function sets the scale for the
+ * current render target.
+ *
  * \param renderer the rendering context.
  * \param scaleX the horizontal scaling factor.
  * \param scaleY the vertical scaling factor.
@@ -1690,6 +1740,9 @@ extern SDL_DECLSPEC bool SDLCALL SDL_SetRenderScale(SDL_Renderer *renderer, floa
 /**
  * Get the drawing scale for the current target.
  *
+ * Each render target has its own scale. This function gets the scale for the
+ * current render target.
+ *
  * \param renderer the rendering context.
  * \param scaleX a pointer filled in with the horizontal scaling factor.
  * \param scaleY a pointer filled in with the vertical scaling factor.