diff --git a/src/main.c b/src/main.c
index 86a7d32..19e1b67 100644
--- a/src/main.c
+++ b/src/main.c
@@ -53,23 +53,32 @@ int main()
 
   glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
 
+  const int buf_width = 4;
+  const int buf_height = 4;
+
   //////////////////////////////////////////////////////////////////////
   // textures
   //////////////////////////////////////////////////////////////////////
 
-  const char * data = "arst";
+  const char * data =
+    "arst"
+    "qwfp"
+    "1234"
+    "6789";
+  int input_width = 4;
+  int input_height = 4;
 
   uint texture_input = make_texture(data,
                                     GL_R8, // internalformat
-                                    2, // width
-                                    2, // height
+                                    input_width,
+                                    input_height,
                                     GL_RED,
                                     GL_UNSIGNED_BYTE);
 
   uint texture_framebuffer = make_texture(NULL,
                                           GL_RGBA32F,
-                                          2,
-                                          2,
+                                          buf_width,
+                                          buf_height,
                                           GL_RGBA,
                                           GL_UNSIGNED_BYTE);
 
@@ -83,6 +92,8 @@ int main()
                                      src_shader_test_vs_glsl_size,
                                      src_shader_test_fs_glsl_start,
                                      src_shader_test_fs_glsl_size);
+  uint program_test__tex_sampler = glGetUniformLocation(program_test, "tex_sampler");
+  uint program_test__tex_size = glGetUniformLocation(program_test, "tex_size");
 
   //////////////////////////////////////////////////////////////////////
   // buffers
@@ -111,12 +122,56 @@ int main()
     if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
       glfwSetWindowShouldClose(window, true);
 
-    /*
+    //
+
     glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
+    glViewport(0, 0, buf_width, buf_height);
+
+    glClearColor(0.78, 0.56, 0.34, 0.12);
+    glClear(GL_COLOR_BUFFER_BIT);
+
+    glActiveTexture(GL_TEXTURE0);
+    glBindTexture(GL_TEXTURE_2D, texture_input);
     uint draw_buffers[1] = {GL_COLOR_ATTACHMENT0};
     glDrawBuffers(1, draw_buffers);
-    glViewport(0, 0, 2, 2);
-    */
+    glUseProgram(program_test);
+    glUniform1i(program_test__tex_sampler, 0);
+    glUniform4f(program_test__tex_size,
+                input_width, input_height,
+                0.5f / input_width,
+                0.5f / input_height);
+    glBindVertexArray(vertex_array);
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+
+    float out[4 * buf_width * buf_height] = {};
+    glReadPixels(0, 0,
+                 buf_width, buf_height,
+                 GL_RGBA,
+                 GL_FLOAT,
+                 out);
+
+    for (int y = 0; y < buf_height; y++) {
+      for (int x = 0; x < buf_width; x++) {
+        printf("[% 2.3f % 2.3f % 2.3f % 2.3f ] ",
+               out[(y * buf_width + x) * 4 + 0],
+               out[(y * buf_width + x) * 4 + 1],
+               out[(y * buf_width + x) * 4 + 2],
+               out[(y * buf_width + x) * 4 + 3]);
+      }
+      printf("\n");
+    }
+    int sum = 0;
+    for (int i = 0; i < buf_width * buf_height; i++) {
+      printf("%d ", data[i]);
+      if ((i % 4) == 3)
+        printf("\n");
+      sum += data[i];
+    }
+    printf("sum: %d\n", sum);
+    break;
+
+    /*
+    glBindFramebuffer(GL_FRAMEBUFFER, 0);
     glViewport(0, 0, vp_width, vp_height);
 
     glClearColor(0.1, 0.2, 0.0, 0.4);
@@ -125,24 +180,11 @@ int main()
     glUseProgram(program_test);
     glBindVertexArray(vertex_array);
     glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+    */
 
     //glFlush();
     //glFinish();
 
-    /*
-    float out[4 * 2 * 2] = {0};
-    glReadPixels(0, 0,
-                 2, 2,
-                 GL_RGBA,
-                 GL_FLOAT,
-                 out);
-
-    for (int i = 0; i < 4 * 2 * 2; i++) {
-      printf("%f\n", out[i]);
-    }
-    */
-    //printf("swap\n");
-
     glfwSwapBuffers(window);
     glfwPollEvents();
   }
diff --git a/src/shader/test.fs.glsl b/src/shader/test.fs.glsl
index b4b046e..4a02ae7 100644
--- a/src/shader/test.fs.glsl
+++ b/src/shader/test.fs.glsl
@@ -2,9 +2,24 @@
 
 out vec4 fragment_color;
 
+uniform sampler2D tex_sampler;
+uniform vec4 tex_size;
+
 in vec2 f_position;
 
 void main()
 {
-  fragment_color = vec4(f_position, 0, 0);
+  vec4 p = texture(tex_sampler, f_position);
+
+  float sum = 0;
+  for (float y = 0; y < tex_size.y; y++) {
+    for (float x = 0; x < tex_size.x; x++) {
+      vec2 coord = vec2((x * 2 + 1) * tex_size.z,
+                        (y * 2 + 1) * tex_size.w);
+
+      sum += texture(tex_sampler, coord).x * 255;
+    }
+  }
+
+  fragment_color = vec4(p.x * 255, sum, f_position);
 }
diff --git a/src/shader/test.vs.glsl b/src/shader/test.vs.glsl
index e1b1518..37fea77 100644
--- a/src/shader/test.vs.glsl
+++ b/src/shader/test.vs.glsl
@@ -6,7 +6,7 @@ out vec2 f_position;
 
 void main()
 {
-  f_position = position;
+  f_position = position * 0.5 + 0.5;
 
   gl_Position = vec4(position, 0, 1);
 }