diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2ab8bbd..07a11c2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -47,7 +47,7 @@ if (WIN32)
     )
 endif()
 
-#set(CMAKE_CXX_FLAGS "-O3 -Wall -Wextra")
+set(CMAKE_CXX_FLAGS "-O3 -Wall -Wextra")
 
 file(COPY "assets" DESTINATION "${PROJECT_BINARY_DIR}")
 file(GLOB_RECURSE ASSETS  "assets/*")
diff --git a/assets/shader_programs/test_fragment.glsl b/assets/shader_programs/test_fragment.glsl
index b813979..3607003 100644
--- a/assets/shader_programs/test_fragment.glsl
+++ b/assets/shader_programs/test_fragment.glsl
@@ -1,7 +1,55 @@
 #version 120
 
+// The color manually set with glColor4f, glColor4ubv etc.
 varying vec4 v_color;
 
-void main(){
+// The number of texture units that have been set.
+uniform int TEXTURE_UNIT_SET_COUNT;
+
+// True if we should perform the alpha mask operation.
+uniform bool ALPHA_MASK;
+
+// True if we're rendering text.
+uniform bool TEXT;
+
+// Texture unit 0 - 7 (8 - 31 will come later).
+uniform sampler2D GL_TEXTURE0;
+uniform sampler2D GL_TEXTURE1;
+uniform sampler2D GL_TEXTURE2;
+uniform sampler2D GL_TEXTURE3;
+uniform sampler2D GL_TEXTURE4;
+uniform sampler2D GL_TEXTURE5;
+uniform sampler2D GL_TEXTURE6;
+uniform sampler2D GL_TEXTURE7;
+
+// Texture coordinates.
+varying vec2 GL_TEXTURE0_COORD;
+varying vec2 GL_TEXTURE1_COORD;
+varying vec2 GL_TEXTURE2_COORD;
+varying vec2 GL_TEXTURE3_COORD;
+varying vec2 GL_TEXTURE4_COORD;
+varying vec2 GL_TEXTURE5_COORD;
+varying vec2 GL_TEXTURE6_COORD;
+varying vec2 GL_TEXTURE7_COORD;
+
+void DrawColorOnly() {
     gl_FragColor = v_color;
+}
+
+// TODO fix positive alpha mask.
+void SampleTextureUnits() {
+    if (TEXT)
+        gl_FragColor = vec4(v_color.rgb, v_color.a * texture2D(GL_TEXTURE0, GL_TEXTURE0_COORD).a);
+
+    // Draw sprite, partial sprite, mirror sprite, render target, partial render target.
+    else if (TEXTURE_UNIT_SET_COUNT == 1)
+        gl_FragColor = v_color * texture2D(GL_TEXTURE0, GL_TEXTURE0_COORD);
+}
+
+void main() {
+    if (TEXTURE_UNIT_SET_COUNT == 0) {
+        DrawColorOnly(); return;
+    }
+
+    SampleTextureUnits();
 }
\ No newline at end of file
diff --git a/assets/shader_programs/test_vertex.glsl b/assets/shader_programs/test_vertex.glsl
index 1fb19a9..e1fcb80 100644
--- a/assets/shader_programs/test_vertex.glsl
+++ b/assets/shader_programs/test_vertex.glsl
@@ -3,7 +3,27 @@
 // The color manually set with glColor4f, glColor4ubv etc etc.
 varying vec4 v_color;
 
+// The texture coordinates in each texture unit.
+varying vec2 GL_TEXTURE0_COORD;
+varying vec2 GL_TEXTURE1_COORD;
+varying vec2 GL_TEXTURE2_COORD;
+varying vec2 GL_TEXTURE3_COORD;
+varying vec2 GL_TEXTURE4_COORD;
+varying vec2 GL_TEXTURE5_COORD;
+varying vec2 GL_TEXTURE6_COORD;
+varying vec2 GL_TEXTURE7_COORD;
+
+
 void main() {
     v_color = gl_Color;
+    GL_TEXTURE0_COORD = gl_MultiTexCoord0.xy;
+    GL_TEXTURE1_COORD = gl_MultiTexCoord1.xy;
+    GL_TEXTURE2_COORD = gl_MultiTexCoord2.xy;
+    GL_TEXTURE3_COORD = gl_MultiTexCoord3.xy;
+    GL_TEXTURE4_COORD = gl_MultiTexCoord4.xy;
+    GL_TEXTURE5_COORD = gl_MultiTexCoord5.xy;
+    GL_TEXTURE6_COORD = gl_MultiTexCoord6.xy;
+    GL_TEXTURE7_COORD = gl_MultiTexCoord7.xy;
+
     gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
 }
diff --git a/main.cpp b/main.cpp
index 3cb8d35..695ce52 100644
--- a/main.cpp
+++ b/main.cpp
@@ -133,7 +133,7 @@ public:
         image = new Texture("assets/sprites/Re3D.png", FilteringMode::MIPMAP_NEAREST, JGL::SampleRate::X16);
         image_mask = new Texture("assets/sprites/alpha_mask_2.png");
         j2d_render_target = new RenderTarget({540, 500}, {0,0,0,0}, false,
-                                             SampleRate::X0, FilteringMode::MIPMAP_TRILINEAR);
+                                             SampleRate::NONE, FilteringMode::MIPMAP_NEAREST);
 
         //Texture::MultiplyByAlphaMask(*image, *image_mask);
 
@@ -145,7 +145,6 @@ public:
     float pulse = 0;
     float sprite_radians = 0;
     bool fov_increasing = true;
-    int blit_pos = 0;
 
     void display() {
 
@@ -176,7 +175,7 @@ public:
         camera->render();
         // All 3D elements of the scene and JGL elements *must* be rendered before the 2D stuff
         /* if rendering to screen space directly. */
-        auto test_light = PointLight({2,1,2}, {pulse,pulse,pulse, 255}, {pulse, pulse, pulse, 255}, {0,0,0}, 1, 0.1, 0.01);
+        auto test_light = PointLight({2,1,2}, {(u8) pulse,(u8) pulse,(u8) pulse, 255}, {(u8) pulse, (u8) pulse, (u8) pulse, 255}, {0,0,0}, 1, 0.1, 0.01);
         // If a 3D object has transparency. The things you'd like to see through it must be drawn before.
 
         J3D::Begin();
@@ -191,7 +190,7 @@ public:
             J3D::WireframeAABB(Colors::Yellow, {0.5, 0, 0.5}, {0.125, 0.125, 0.125}, 1);
         J3D::End();
 
-        J2D::Begin(nullptr, &shader, true);
+        J2D::Begin(j2d_render_target, &shader, true);
             J2D::FillRect(Colors::Blue, {0,52}, {100,100});
             J2D::DrawSprite(image, {300, 400}, sprite_radians * 0.10f, {0.5,0.5}, {1, 1}, Colors::White);
             J2D::DrawMirrorSprite(image, {400, 300}, Direction::Horizontal | Direction::Vertical, sprite_radians, {0.5,0.5}, {1, 1}, Colors::White);
@@ -231,12 +230,12 @@ public:
 
         J2D::End();
 
-        /*
-        J2D::Begin();
-            //J2D::DrawRenderTarget(j2d_render_target, {0, 0});
-            //J2D::DrawSprite(image, image_mask, {0, 0}, 0.25, {0.5, 0.5}, {1,1});
+
+        J2D::Begin(nullptr, &shader, true);
+            J2D::DrawRenderTarget(j2d_render_target, {0, 0});
+            J2D::DrawSprite(image, image_mask, {0, 0}, 0.25, {0.5, 0.5}, {1,1});
         J2D::End();
-         */
+
 
 
 
diff --git a/src/renderer/OpenGL/J2D.cpp b/src/renderer/OpenGL/J2D.cpp
index b6e8447..76cde18 100644
--- a/src/renderer/OpenGL/J2D.cpp
+++ b/src/renderer/OpenGL/J2D.cpp
@@ -427,9 +427,14 @@ void J2D::DrawSprite(const Texture& texture, const Texture& alpha_mask, const Ve
     glVertexPointer(2, GL_FLOAT, sizeof(Vector2), vertices.data());
     glTexCoordPointer(2, GL_FLOAT, sizeof(Vector2), textureCoordinates.data());
 
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 2);
     // Draw.
     glDrawArrays(GL_QUADS, 0, 4);
 
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 0);
+
     // Reset Texture 1.
     glBindTexture(GL_TEXTURE_2D, 0);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
@@ -551,11 +556,18 @@ void J2D::DrawSprite(const Texture& texture, const Vector2& pos, float rad_rotat
     glBindTexture(GL_TEXTURE_2D, texture.GetHandle());
     glVertexPointer(2, GL_FLOAT, sizeof(Vector2), vertices.data());
     glTexCoordPointer(2, GL_FLOAT, sizeof(Vector2), textureCoordinates.data());
+
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 1);
+
     glDrawArrays(GL_QUADS, 0, 4);
     glBindTexture(GL_TEXTURE_2D, 0);
     glColor4fv(default_state.draw_color);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
     glDisable(GL_TEXTURE_2D);
+
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 0);
 }
 
 
@@ -640,7 +652,15 @@ void J2D::DrawPartialSprite(const Texture& texture, const Vector2& position, con
     glBindTexture(GL_TEXTURE_2D, texture.GetHandle());
     glVertexPointer(2, GL_FLOAT, sizeof(Vector2), vertices.data());
     glTexCoordPointer(2, GL_FLOAT, 0, textureCoordinates.data());
+
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 1);
+
     glDrawArrays(GL_QUADS, 0, 4);
+
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 0);
+
     glBindTexture(GL_TEXTURE_2D, 0);
     glColor4fv(default_state.draw_color);
     glDisableClientState(GL_TEXTURE_COORD_ARRAY);
@@ -722,8 +742,15 @@ void J2D::DrawMirrorSprite(const Texture& texture, const Vector2& position, Dire
     glColor4ubv(color.ptr());
     glVertexPointer(2, GL_FLOAT, sizeof(Vector2), vertices.data());
     glTexCoordPointer(2, GL_FLOAT, sizeof(Vector2), textureCoordinates.data());
+
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 1);
+
     glDrawArrays(GL_QUADS, 0, 4);
 
+    if (current_state.current_shader)
+        current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 0);
+
     //Reset the wrapping mode.
     if (texture.GetWrappingMode() == WrappingMode::CLAMP_TO_EDGE)
         glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE),
diff --git a/src/renderer/OpenGL/TextRendering.cpp b/src/renderer/OpenGL/TextRendering.cpp
index 4db8b27..51f1f5f 100644
--- a/src/renderer/OpenGL/TextRendering.cpp
+++ b/src/renderer/OpenGL/TextRendering.cpp
@@ -156,7 +156,17 @@ namespace JGL {
         }
         glVertexPointer(2, GL_FLOAT, sizeof(Vector2), vertices.data());
         glTexCoordPointer(2, GL_FLOAT, sizeof(Vector2), texcoords.data());
+
+        if (current_state.current_shader)
+            current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 1),
+            current_state.current_shader->SetBool("TEXT", true);
+
         glDrawArrays(GL_TRIANGLES, 0, (int) vertices.size() * 6);
+
+        if (current_state.current_shader)
+            current_state.current_shader->SetInt("TEXTURE_UNIT_SET_COUNT", 0),
+            current_state.current_shader->SetBool("TEXT", false);
+
         glBindTexture(GL_TEXTURE_2D, 0);
         glColor4fv(default_state.draw_color);
         glDisableClientState(GL_TEXTURE_COORD_ARRAY);
@@ -238,8 +248,14 @@ namespace JGL {
             glEnable(GL_CULL_FACE);
             glCullFace(GL_BACK);
 
+        if (current_state.current_shader)
+            current_state.current_shader->SetBool("TEXT", true);
+
         glDrawArrays(GL_TRIANGLES, 0, (int) vertices.size() * 6);
 
+        if (current_state.current_shader)
+            current_state.current_shader->SetBool("TEXT", false);
+
         if (!draw_back_face)
             glDisable(GL_CULL_FACE);