Add an option in mjrContext for mjr_readPixels output format.

PiperOrigin-RevId: 500342924
Change-Id: I43e8c6208db341e2bdbef10382b7293c35bdca65

src/render/render_context.c

@@ -1602,6 +1602,9 @@ void mjr_makeContext_offSize(const mjModel* m, mjrContext* con, int fontscale,
   while ((err = glGetError())) {
     mju_warning_i("OpenGL error 0x%x in or before mjr_makeContext", err);
   }
+
+  // set default color pixel format for mjr_readPixels
+  con->readPixelFormat = GL_RGB;
 }
 
 

src/render/render_gl2.c

@@ -153,7 +153,7 @@ void mjr_readPixels(unsigned char* rgb, float* depth,
     // read rgb and depth
     if (rgb) {
       glReadPixels(viewport.left, viewport.bottom, viewport.width, viewport.height,
-                   GL_RGB, GL_UNSIGNED_BYTE, rgb);
+                   con->readPixelFormat, GL_UNSIGNED_BYTE, rgb);
     }
     if (depth) {
       glReadPixels(viewport.left, viewport.bottom, viewport.width, viewport.height,