In bringing Modern Warfare's visuals up to modern standards, enhancements to the environments were designed using a procedure called "paint-over": color schemes were established and screenshots taken of the levels from Modern Warfare before they were overlaid with concept art.[6] Raven wanted to give the environments a sense of history to avoid them feeling generic, with more visual details being integrated into them.[6][29][31] The game used improved textures and mapping, effects, and lighting;[31] objects were remodeled and new features such as realistic physics were used to move materials like clothing.[5][6][31] The remaster became the first Call of Duty game to allow each gun to eject spent ammunition rounds accurate to that type, which was achieved through the inserted rounds remaining in the gun before ejection; identical rounds separate from those inserted were ejected in previous games.[6] Raven faced some issues remastering the graphics, as the remaster used a heavily upgraded version of the series' engine. As a result, several of Modern Warfare's visual assets were not suited to the new technology, requiring the developers to enhance or remake them.[4] The movement of non-player characters was improved to be more realistic. Several new first-person animations were added to the single-player campaign for immersion during certain scenes[34] and to improve how the camera made use of the player character's body.[5]