Disclosure: This draft was generated with AI and checked against the cited primary sources, with a separate AI editorial review. It was prepared for the FrameSprite team, which has a commercial interest in FrameSprite. Proposed examples are not executed tests unless explicitly identified as recorded fixture results.
Use SDL_GetRenderOutputSize for the renderer's true output size, ignoring a current texture target and logical presentation. Use SDL_GetCurrentRenderOutputSize when the current target and its logical adjustments matter. Allocating a preview from the wrong query can give it the window's dimensions. The distinction is explicit in SDL_GetRenderOutputSize.
Key Takeaways
- Name every size by its domain: window output, active target or source texture.
- Query at the point where the intended target state is known.
- Reallocate only when the required target size actually changes.
Write down the allocation requirement
A portrait preview may need a fixed 256 by 256 output regardless of the window size. A full-window postprocess target may instead need to track the actual renderer output. Do not feed both cases through an ambiguously named getSize helper.
Create a short record with intended preview size, renderer output size, current render-target size and source image size. A 2048-pixel sheet does not require a 2048-pixel portrait target if only a small frame is displayed.
The texture-memory guide explains why target dimensions deserve an explicit budget instead of automatically copying the largest input.
Query the correct domain
The following fragment compares two documented queries:
/* SDL 3.2+ fragment; not compiled or run here. */
int output_w = 0, output_h = 0;
int current_w = 0, current_h = 0;
if (!SDL_GetRenderOutputSize(renderer, &output_w, &output_h) ||
!SDL_GetCurrentRenderOutputSize(renderer, ¤t_w, ¤t_h)) {
SDL_Log("Size query failed: %s", SDL_GetError());
}
The current-output query describes its current-target and logical-size behavior. Log which target was active when you called it. A size captured before changing targets should not be treated as if it describes the later target.
For source texture dimensions, use SDL_GetTextureSize instead. Source dimensions describe which pixels can be sampled; they do not define the resolution of every destination.
Avoid a resize feedback loop
An application can accidentally read the size of its existing preview target, use that to choose a new target, and then requery it after applying logical sizing. Keep desired size as application state with a clear owner.
Only replace the target when that desired size changes. Confirm the replacement succeeded before abandoning the old resource, and update every consumer of the preview image. Do not allocate a new target on every draw merely because a size query is inexpensive.
| Requirement | Size source |
|---|---|
| Fixed portrait export | Explicit application output size |
| Window-resolution target | True renderer output |
| Work tied to active logical target | Current-output contract |
| Slice an imported sheet | Source texture dimensions |
For restoring the target after drawing a preview, use the SDL3 target-state guide. Size selection does not replace that state restoration.
Acceptance across output changes
Test a window resize, a high-density display and a deliberately small texture target. Record all queried sizes and compare them with the preview's actual dimensions. Verify a fixed-resolution export stays fixed when that is the intended requirement.
Keep pointer-coordinate conversion separate; the SDL3 logical-click guide addresses input mapping. No display or allocation test was executed here. This article targets the documented SDL 3.2+ query APIs and does not predict a particular platform's pixel ratio.
Keep allocation decisions out of incidental draw state
Calculate a fixed export's desired dimensions from its export settings, not from whichever renderer target a helper happens to find active. A scene may render portraits, world content and interface controls at different resolutions during one frame. If a query is needed, call it while the owning pass is active and name the stored result accordingly. Reject zero or otherwise invalid sizes before allocation. This makes the size contract reviewable when a later rendering feature adds another target to the frame.
Sources and editorial ownership
Primary references checked on October 20, 2026:
Editorial owner: FrameSprite Workflow Team. Editorial and verification policy. Report a documentation correction.
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