Support reversed Z rendering and float32 offscreen depth buffer

Combined, both options greatly improve camera depth accuracy compared to
OpenGL default Z mapping and int24 depth buffer.

Requires GL_ARB_clip_control and ARB_depth_buffer_float extensions

include/mujoco/mjrender.h

@@ -39,6 +39,15 @@ typedef enum mjtFramebuffer_ {    // OpenGL framebuffer option
   mjFB_OFFSCREEN                  // offscreen buffer
 } mjtFramebuffer;
 
+typedef enum mjtDepthMapping_ {   // OpenGL depth buffer mapping (from znear to zfar)
+  mjDB_NEGONETOONE  = 0,          // Negative one to one (OpenGL default)
+  mjDB_ONETOZERO                  // Reversed Z buffer (decreases numerical error)
+} mjtDepthMapping;
+
+typedef enum mjtDepthPrecision_ { // OpenGL depth buffer precision
+  mjDB_INT24        = 0,          // 24 bit integer buffer (OpenGL default)
+  mjDB_FLOAT32                    // 32 bit float buffer
+} mjtDepthPrecision;
 
 typedef enum mjtFontScale_ {      // font scale, used at context creation
   mjFONTSCALE_50      = 50,       // 50% scale, suitable for low-res rendering
@@ -151,6 +160,12 @@ struct mjrContext_ {              // custom OpenGL context
 
   // pixel output format
   int     readPixelFormat;        // default color pixel format for mjr_readPixels
+
+  // depth buffer mode
+  int     depthMapping;           // depth buffer mapping from [znear zfar] to normalized device coordinates: mjDB_NEGONETOONE or mjDB_ONETOZERO
+
+  // depth buffer precision
+  int     depthPrecision;         // depth buffer precision: mjDB_INT24 or mjDB_FLOAT32
 };
 typedef struct mjrContext_ mjrContext;