Vulkan: cache main color extent for stable render-target queries (#128)

Store main FBO color attachment dimensions when attachments are built and
have vk_get_render_target_width/height prefer them while FBO is active.
Auxiliary passes that temporarily overwrite vk.renderWidth no longer skew
Forward+, post params, temporal resets, or scissor clamping.

Document the behavior in RENDERER_2026_ARCHITECTURE_PASS.md.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: timfox

docs/RENDERER_2026_ARCHITECTURE_PASS.md

@@ -100,6 +100,7 @@ Treat temporal stability as a first-class renderer subsystem instead of a set of
 ### Incremental (engine)
 
 - **`VK_TEMPORAL_RESET_RENDER_SIZE_CHANGE`** in `vk_temporal.c` compares the **effective render target** size from **`vk_get_render_target_width()` / `vk_get_render_target_height()`** (FBO / `r_renderScale`), not `glConfig` alone, so internal resolution changes still clear motion, TAA, volumetric, exposure, and occlusion history consistently with the color pass.
+- When **`vk.fboActive`**, those helpers prefer **`vk.mainColorWidth` / `vk.mainColorHeight`** (set when the main scene color attachment is created in `vk_attachments.c`) so **Forward+**, **post params**, and **temporal** paths do not read transient **`vk.renderWidth`** overrides from shadow or atlas passes.
 
 ### Explicit non-goals
 

src/renderers/vulkan/vk.h

@@ -1271,6 +1271,9 @@ typedef struct {
 
 	uint32_t renderWidth;
 	uint32_t renderHeight;
+	/* Main scene color attachment (FBO) pixel size; stable while vk.renderWidth is temporarily overridden (shadow atlases, etc.). */
+	uint32_t mainColorWidth;
+	uint32_t mainColorHeight;
 
 	float renderScaleX;
 	float renderScaleY;

src/renderers/vulkan/vk_attachments.c

@@ -507,6 +507,8 @@ void vk_create_attachments( void )
 		// post-processing/msaa-resolve
 			vk_create_fullres_color_attachment( vk.color_format,
 				copyableColorUsage, &vk.color_image, &vk.color_image_view, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, qfalse );
+			vk.mainColorWidth = fullWidth;
+			vk.mainColorHeight = fullHeight;
 			vk_create_fullres_color_attachment( vk.color_format,
 				VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_SAMPLED_BIT,
 				&vk.ui_overlay_image, &vk.ui_overlay_image_view, VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL, qfalse );
@@ -1866,6 +1868,8 @@ void vk_destroy_attachments( void )
 		vk.color_image_view = VK_NULL_HANDLE;
 		vk.post_fog_color_source = VK_NULL_HANDLE;
 		vk.scene_post_fog_color_source = VK_NULL_HANDLE;
+		vk.mainColorWidth = 0u;
+		vk.mainColorHeight = 0u;
 	}
 	if ( vk.ui_overlay_image ) {
 		qvkDestroyImage( vk.device, vk.ui_overlay_image, NULL );

src/renderers/vulkan/vk_view_state.c

@@ -23,6 +23,9 @@ static qboolean vk_curr_entity_model_valid[MAX_REFENTITIES];
 
 uint32_t vk_get_render_target_width( void )
 {
+	if ( vk.fboActive && vk.mainColorWidth > 0u ) {
+		return vk.mainColorWidth;
+	}
 	if ( vk.renderWidth > 0 ) {
 		return vk.renderWidth;
 	}
@@ -34,6 +37,9 @@ uint32_t vk_get_render_target_width( void )
 
 uint32_t vk_get_render_target_height( void )
 {
+	if ( vk.fboActive && vk.mainColorHeight > 0u ) {
+		return vk.mainColorHeight;
+	}
 	if ( vk.renderHeight > 0 ) {
 		return vk.renderHeight;
 	}