From 48d275a01baaff68a0c055dd77664b5d0f22d70d Mon Sep 17 00:00:00 2001
From: Andreas Grois <andi@grois.info>
Date: Sat, 10 Mar 2018 00:14:46 +0100
Subject: Dump result to image.png in current folder.

---
 BuddhaTest/CMakeLists.txt     |  8 ++++--
 BuddhaTest/include/Helpers.h  |  5 +++-
 BuddhaTest/src/BuddhaTest.cpp | 13 +++++++--
 BuddhaTest/src/Helpers.cpp    | 64 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 84 insertions(+), 6 deletions(-)

diff --git a/BuddhaTest/CMakeLists.txt b/BuddhaTest/CMakeLists.txt
index d58d00a..be7d4d6 100644
--- a/BuddhaTest/CMakeLists.txt
+++ b/BuddhaTest/CMakeLists.txt
@@ -10,6 +10,8 @@ configure_file("Shaders/BuddhaCompute.glsl" ${CMAKE_CURRENT_BINARY_DIR}/Shaders/
 configure_file("Shaders/BuddhaVertex.glsl" ${CMAKE_CURRENT_BINARY_DIR}/Shaders/BuddhaVertex.glsl)
 
 find_package(OpenGL REQUIRED)
-target_include_directories(BuddhaTest PRIVATE "include" ${OPENGL_INCLUDE_DIR})
-target_link_libraries(BuddhaTest glfw ${OPENGL_gl_LIBRARY})
-# on Linux we need to link against libdl. Maybe add id here?
\ No newline at end of file
+find_package(PNG REQUIRED)
+target_include_directories(BuddhaTest PRIVATE "include" ${OPENGL_INCLUDE_DIR} ${PNG_INCLUDE_DIRS})
+target_link_libraries(BuddhaTest glfw ${OPENGL_gl_LIBRARY} ${PNG_LIBRARIES})
+add_definitions(${PNG_DEFINITIONS})
+# on Linux we need to link against libdl. Maybe add id here?
diff --git a/BuddhaTest/include/Helpers.h b/BuddhaTest/include/Helpers.h
index 05ad151..c24e2c7 100644
--- a/BuddhaTest/include/Helpers.h
+++ b/BuddhaTest/include/Helpers.h
@@ -1,9 +1,12 @@
 #pragma once
 #include <glad/glad.h>
 #include <GLFW/glfw3.h>
+#include <vector>
 
 namespace Helpers
 {
 	GLuint LoadShaders(const char * vertex_file_path, const char * fragment_file_path);
 	GLuint LoadComputeShader(const char * compute_file_path);
-}
\ No newline at end of file
+
+    void WriteOutputPNG(const std::vector<uint32_t>& data, unsigned int width, unsigned int height);
+}
diff --git a/BuddhaTest/src/BuddhaTest.cpp b/BuddhaTest/src/BuddhaTest.cpp
index 57edc14..d1b6a66 100644
--- a/BuddhaTest/src/BuddhaTest.cpp
+++ b/BuddhaTest/src/BuddhaTest.cpp
@@ -14,8 +14,8 @@ int main()
     unsigned int bufferWidth = 1600;
     unsigned int bufferHeight = 900;
 
-    unsigned int orbitLengthRed = 100;
-    unsigned int orbitLengthGreen = 10;
+    unsigned int orbitLengthRed = 10;
+    unsigned int orbitLengthGreen = 100;
     unsigned int orbitLengthBlue = 1000;
 
 	GLFWwindow* window;
@@ -124,6 +124,15 @@ int main()
 		glfwPollEvents();
 	}
 
+    glMemoryBarrier(GL_ALL_BARRIER_BITS);
+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, drawBuffer);
+    {
+        const unsigned int pixelCount{(bufferWidth * bufferHeight)*3}; //*3 -> RGB
+        std::vector<uint32_t> readBackBuffer(pixelCount);
+        glGetBufferSubData(GL_SHADER_STORAGE_BUFFER,4*2,4 * pixelCount,readBackBuffer.data()); //offset of 2*4, that's the dimension integers.
+        Helpers::WriteOutputPNG(readBackBuffer,bufferWidth,bufferHeight);
+    }
+
 	glfwTerminate();
 	return 0;
 }
diff --git a/BuddhaTest/src/Helpers.cpp b/BuddhaTest/src/Helpers.cpp
index e9caba9..69dafa3 100644
--- a/BuddhaTest/src/Helpers.cpp
+++ b/BuddhaTest/src/Helpers.cpp
@@ -3,6 +3,7 @@
 #include <fstream>
 #include <sstream>
 #include <vector>
+#include <png.h>
 
 namespace Helpers
 {
@@ -146,4 +147,67 @@ namespace Helpers
 		glDeleteShader(ComputeShaderID);
 		return ProgramID;
 	}
+    void WriteOutputPNG(const std::vector<uint32_t>& data, unsigned int width, unsigned int height)
+    {
+        png_byte ** row_pointers = static_cast<png_byte **>(calloc(height,sizeof(void *)));
+        for(int i = 0; i < height ; ++i)
+        {
+            row_pointers[i] = static_cast<png_byte *>(calloc(3*width,sizeof(png_byte)));
+        }
+
+        uint32_t maxValue{UINT32_C(0)};
+        for(unsigned int i = 0; i < data.size();++i)
+        {
+            maxValue = std::max(maxValue,data[i]);
+        }
+        for(unsigned int i = 0; i < data.size();++i)
+        {
+            unsigned int row = (i)/(3*width);
+            unsigned int col = i - 3*row*width;
+            row_pointers[row][col] = (255*data[i] + (maxValue/2))/maxValue;
+        }
+
+        //beware, this is going to be ugly C syntax, but well, libpng...
+        FILE * fp = fopen("image.png", "wb");
+        if(!fp)
+        {
+            return;
+        }
+        png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
+        if(!png_ptr)
+        {
+            fclose(fp);
+            return;
+        }
+        png_infop info_ptr = png_create_info_struct(png_ptr);
+        if(!info_ptr)
+        {
+            png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
+            fclose(fp);
+            return;
+        }
+        if(setjmp(png_jmpbuf(png_ptr)))
+        {
+            png_destroy_write_struct(&png_ptr, &info_ptr);
+            fclose(fp);
+            return;
+        }
+        png_init_io(png_ptr, fp);
+        png_set_IHDR(png_ptr, info_ptr, width, height, 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+
+        png_write_info(png_ptr, info_ptr);
+        //header written.
+
+        png_write_image(png_ptr, row_pointers);
+
+        png_write_end(png_ptr, info_ptr);
+        png_destroy_write_struct(&png_ptr, &info_ptr);
+
+        for(int i = 0; i < height ; ++i)
+        {
+            free(row_pointers[i]);
+        }
+
+        free(row_pointers);
+    }
 }
-- 
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