[client] egl: implement SDR to HDR mapping for cursors

client/renderers/EGL/cursor.c

@@ -31,6 +31,7 @@
 #include <stdatomic.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 
 // these headers are auto generated by cmake
 #include "cursor.vert.h"
@@ -73,6 +74,10 @@ struct EGL_Cursor
   LG_RendererRotate rotate;
   int               cbMode;
 
+  // HDR state for native compositor HDR with PQ
+  bool              hdrActive;
+  bool              hdrPQ;
+
   _Atomic(struct CursorPos)  pos;
   _Atomic(struct CursorPos)  hs;
   _Atomic(struct CursorSize) size;
@@ -83,6 +88,58 @@ struct EGL_Cursor
   struct EGL_Model * model;
 };
 
+// PQ constants (ST.2084)
+#define PQ_M1 (2610.0f / 16384.0f)
+#define PQ_M2 (2523.0f / 32.0f)
+#define PQ_C1 (3424.0f / 4096.0f)
+#define PQ_C2 (2413.0f / 128.0f)
+#define PQ_C3 (2392.0f / 128.0f)
+#define SDR_WHITE_NITS 203.0f
+
+static float srgb2lin_f(float c)
+{
+  c /= 255.0f;
+  if (c <= 0.04045f)
+    return c / 12.92f;
+  return powf((c + 0.055f) / 1.055f, 2.4f);
+}
+
+static float lin2pq_f(float nits)
+{
+  float y = powf(nits / 10000.0f, PQ_M1);
+  float p = (PQ_C1 + PQ_C2 * y) / (1.0f + PQ_C3 * y);
+  return powf(p, PQ_M2);
+}
+
+static void convertCursorDataToPQ(uint8_t * data, int width, int height,
+    int stride)
+{
+  for (int y = 0; y < height; ++y)
+  {
+    uint8_t * row = data + (size_t)stride * y;
+    for (int x = 0; x < width; ++x)
+    {
+      uint8_t * px = row + (size_t)x * 4;
+      // BGRA order: px[0]=B, px[1]=G, px[2]=R, px[3]=A
+      float b_lin = srgb2lin_f(px[0]);
+      float g_lin = srgb2lin_f(px[1]);
+      float r_lin = srgb2lin_f(px[2]);
+
+      float b_nits = b_lin * SDR_WHITE_NITS;
+      float g_nits = g_lin * SDR_WHITE_NITS;
+      float r_nits = r_lin * SDR_WHITE_NITS;
+
+      float b_pq = lin2pq_f(b_nits);
+      float g_pq = lin2pq_f(g_nits);
+      float r_pq = lin2pq_f(r_nits);
+
+      px[0] = (uint8_t)(b_pq * 255.0f + 0.5f);
+      px[1] = (uint8_t)(g_pq * 255.0f + 0.5f);
+      px[2] = (uint8_t)(r_pq * 255.0f + 0.5f);
+    }
+  }
+}
+
 static bool cursorTexInit(struct CursorTex * t,
     const char * vertex_code  , size_t vertex_size,
     const char * fragment_code, size_t fragment_size)
@@ -256,6 +313,7 @@ struct CursorState egl_cursorRender(EGL_Cursor * cursor,
     cursor->update = false;
 
     uint8_t * data = cursor->data;
+    bool needsPQ = cursor->hdrActive && cursor->hdrPQ;
 
     switch(cursor->type)
     {
@@ -284,6 +342,13 @@ struct CursorState egl_cursorRender(EGL_Cursor * cursor,
 
       case LG_CURSOR_COLOR:
       {
+        // Convert color data from sRGB to PQ when compositor HDR PQ is active.
+        // This is done CPU-side because the shader also handles mask textures
+        // where PQ conversion would break the GL_ZERO/GL_SRC_COLOR blend math.
+        if (needsPQ)
+          convertCursorDataToPQ(data, cursor->width, cursor->height,
+              cursor->stride);
+
         egl_textureSetup(cursor->norm.texture, EGL_PF_BGRA,
             cursor->width, cursor->height, cursor->width, cursor->stride);
         egl_textureUpdate(cursor->norm.texture, data, true);
@@ -310,6 +375,7 @@ struct CursorState egl_cursorRender(EGL_Cursor * cursor,
           }
         }
 
+        // Monochrome cursors use AND/XOR mask textures - never convert to PQ
         egl_textureSetup(cursor->norm.texture, EGL_PF_BGRA,
             cursor->width, cursor->height, cursor->width, sizeof(and[0]));
         egl_textureSetup(cursor->mono.texture, EGL_PF_BGRA,
@@ -429,3 +495,14 @@ struct CursorState egl_cursorRender(EGL_Cursor * cursor,
 
   return state;
 }
+
+void egl_cursorSetHDRState(EGL_Cursor * cursor, bool hdrActive, bool hdrPQ)
+{
+  if (cursor->hdrActive != hdrActive || cursor->hdrPQ != hdrPQ)
+  {
+    cursor->hdrActive = hdrActive;
+    cursor->hdrPQ     = hdrPQ;
+    // Force a re-upload of the cursor texture with the new color space
+    cursor->update = true;
+  }
+}

client/renderers/EGL/cursor.h

@@ -52,3 +52,5 @@ void egl_cursorSetState(EGL_Cursor * cursor, const bool visible,
 
 struct CursorState egl_cursorRender(EGL_Cursor * cursor,
     LG_RendererRotate rotate, int width, int height);
+
+void egl_cursorSetHDRState(EGL_Cursor * cursor, bool hdrActive, bool hdrPQ);

client/renderers/EGL/egl.c

@@ -627,8 +627,11 @@ static bool egl_onFrameFormat(LG_Renderer * renderer, const LG_RendererFormat fo
   // (e.g., compositor missing required primaries), keep tone-mapping on.
   bool nativeHDR = false;
   app_getProp(LG_DS_NATIVE_HDR, &nativeHDR);
-  egl_desktopSetNativeHDR(this->desktop,
-      format.hdr && nativeHDR && !app_getHDRDescFailed());
+  bool useNativeHDR = format.hdr && nativeHDR && !app_getHDRDescFailed();
+  egl_desktopSetNativeHDR(this->desktop, useNativeHDR);
+
+  // Tell the cursor shader about HDR state so it can do SDR→PQ conversion
+  egl_cursorSetHDRState(this->cursor, useNativeHDR, format.hdrPQ);
 
   egl_update_scale_type(this);
   egl_damageSetup(this->damage, format.frameWidth, format.frameHeight);