Add lovr.graphics.setProjection;

It's not very good.  It only takes Transforms and sets the projection
for both eyes.  And the projection gets reset at the beginning and
end of lovr.headset.renderTo.  It's meant to be a backdoor.

src/api/graphics.c

@@ -13,6 +13,7 @@
 #include "data/textureData.h"
 #include "data/vertexData.h"
 #include "filesystem/filesystem.h"
+#include "math/transform.h"
 #include "util.h"
 #define _USE_MATH_DEFINES
 #include <math.h>
@@ -584,6 +585,12 @@ static int l_lovrGraphicsTransform(lua_State* L) {
   return 0;
 }
 
+static int l_lovrGraphicsSetProjection(lua_State* L) {
+  Transform* transform = luax_checktype(L, 1, Transform);
+  lovrGraphicsSetProjection(transform->matrix);
+  return 0;
+}
+
 // Rendering
 
 static int l_lovrGraphicsClear(lua_State* L) {
@@ -1302,6 +1309,7 @@ static const luaL_Reg lovrGraphics[] = {
   { "rotate", l_lovrGraphicsRotate },
   { "scale", l_lovrGraphicsScale },
   { "transform", l_lovrGraphicsTransform },
+  { "setProjection", l_lovrGraphicsSetProjection },
 
   // Rendering
   { "clear", l_lovrGraphicsClear },

src/graphics/graphics.c

@@ -361,6 +361,11 @@ void lovrGraphicsMatrixTransform(mat4 transform) {
   mat4_multiply(state.transforms[state.transform], transform);
 }
 
+void lovrGraphicsSetProjection(mat4 projection) {
+  mat4_set(state.camera.projection[0], projection);
+  mat4_set(state.camera.projection[1], projection);
+}
+
 // Rendering
 
 VertexPointer lovrGraphicsGetVertexPointer(uint32_t count) {

src/graphics/graphics.h

@@ -206,6 +206,7 @@ void lovrGraphicsTranslate(float x, float y, float z);
 void lovrGraphicsRotate(float angle, float ax, float ay, float az);
 void lovrGraphicsScale(float x, float y, float z);
 void lovrGraphicsMatrixTransform(mat4 transform);
+void lovrGraphicsSetProjection(mat4 projection);
 
 // Rendering
 VertexPointer lovrGraphicsGetVertexPointer(uint32_t capacity);