Split buffer in three, one per color (as OpenGL guarantees that one can at least have 8 SSBOs), to allow three times larger images. Also make it possible to ignore maximum buffer size reported by the driver.

The maximum buffer size limitation is rather strict on radeonsi, so I decided to split the buffer in three, effectively increasing the maximum image size by a factor of three.
While doing so I realized that at least on radeonsi the reported maximum buffer size seems to be off. For this reason I added a new command line switch, that allows to ignore the maximum buffer size check.
For those curious: radeonsi reports a maximum buffer size of 128 MB, but I had no problems when using three buffers of 1098 MB each.

2 files changed, 33 insertions, 18 deletions

diff --git a/BuddhaTest/src/BuddhaTest.cpp b/BuddhaTest/src/BuddhaTest.cpp
index 1709853..5d03ad4 100644
--- a/BuddhaTest/src/BuddhaTest.cpp
+++ b/BuddhaTest/src/BuddhaTest.cpp
@@ -58,7 +58,7 @@ int main(int argc, char * argv[])
 

     //we have a context. Let's check if input is sane.

     //calcualte buffer size, and make sure it's allowed by the driver.

-    const unsigned int pixelCount{(settings.imageWidth * bufferHeight)*3}; //*3 -> RGB

+    const unsigned int pixelCount{(settings.imageWidth * bufferHeight)};

     if(!settings.CheckValidity())

     {

         glfwTerminate();

@@ -109,15 +109,18 @@ int main(int argc, char * argv[])
 	glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

 

 

-	GLuint drawBuffer;

-	glGenBuffers(1, &drawBuffer);

-	glBindBuffer(GL_SHADER_STORAGE_BUFFER, drawBuffer);

+    GLuint drawBuffer[3];

+    glGenBuffers(3, drawBuffer);

+    for(int i=0; i < 3; ++i)

     {

-        glBufferData(GL_SHADER_STORAGE_BUFFER, 4 * pixelCount, nullptr, GL_DYNAMIC_COPY);

-        glClearBufferData(GL_SHADER_STORAGE_BUFFER,GL_R8,GL_RED,GL_UNSIGNED_INT,nullptr);

+        glBindBuffer(GL_SHADER_STORAGE_BUFFER, drawBuffer[i]);

+        {

+            glBufferData(GL_SHADER_STORAGE_BUFFER, 4 * pixelCount, nullptr, GL_DYNAMIC_COPY);

+            glClearBufferData(GL_SHADER_STORAGE_BUFFER,GL_R8,GL_RED,GL_UNSIGNED_INT,nullptr);

+        }

+        glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2+i, drawBuffer[i]);

     }

-	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, drawBuffer);

-	glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);

+    glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);

 

     uint32_t iterationCount{0};

     glUseProgram(ComputeShader);

@@ -188,17 +191,25 @@ int main(int argc, char * argv[])
     if(!settings.pngFilename.empty())

     {

         glMemoryBarrier(GL_ALL_BARRIER_BITS);

-        glBindBuffer(GL_SHADER_STORAGE_BUFFER, drawBuffer);

+        std::vector<std::vector<uint32_t>> readBackBuffers(3,std::vector<uint32_t>(pixelCount));

+        for(int i = 0; i < 3; ++i)

+        {

+            glBindBuffer(GL_SHADER_STORAGE_BUFFER, drawBuffer[i]);

+            glGetBufferSubData(GL_SHADER_STORAGE_BUFFER,0,4 * pixelCount,readBackBuffers[i].data());

+        }

+

+        //too lazy to change WriteOutputPng...

+        std::vector<uint32_t> combinedBuffer(3*pixelCount);

+        for(int i=0;i<3*pixelCount;++i)

         {

-            std::vector<uint32_t> readBackBuffer(pixelCount);

-            glGetBufferSubData(GL_SHADER_STORAGE_BUFFER,0,4 * pixelCount,readBackBuffer.data());

-            Helpers::WriteOutputPNG(settings.pngFilename,readBackBuffer,settings.imageWidth,bufferHeight, settings.pngGamma, settings.pngColorScale);

+            combinedBuffer[i] = readBackBuffers[i%3][i/3];

         }

+        Helpers::WriteOutputPNG(settings.pngFilename,combinedBuffer,settings.imageWidth,bufferHeight, settings.pngGamma, settings.pngColorScale);

     }

 

     //a bit of cleanup

     glDeleteBuffers(1,&vertexbuffer);

-    glDeleteBuffers(1,&drawBuffer);

+    glDeleteBuffers(3,drawBuffer);

 

 	glfwTerminate();

 	return 0;

diff --git a/BuddhaTest/src/Helpers.cpp b/BuddhaTest/src/Helpers.cpp
index e1a4115..3cb786c 100644
--- a/BuddhaTest/src/Helpers.cpp
+++ b/BuddhaTest/src/Helpers.cpp
@@ -264,10 +264,12 @@ namespace Helpers
         }

         int maxSSBOSize;

         glGetIntegerv(GL_MAX_SHADER_STORAGE_BLOCK_SIZE,&maxSSBOSize);

-        if((static_cast<unsigned long>(imageWidth) * static_cast<unsigned long>(imageHeight)) > static_cast<unsigned long>(maxSSBOSize)/6)

+        if((static_cast<unsigned long>(imageWidth) * static_cast<unsigned long>(imageHeight)) > static_cast<unsigned long>(maxSSBOSize)/2) //divided by 2, as we have 4 bytes per int, but only half the image height

         {

-            std::cerr << "Requested buffer size larger than maximum allowed by graphics driver. Max pixel number: " << maxSSBOSize/6 << std::endl;

-            return false;

+            std::cerr << "Requested buffer size is larger than maximum allowed by graphics driver. Max pixel number: " << maxSSBOSize/2 << std::endl;

+            std::cerr << "You can override this limit check using the --ignoreMaxBufferSize 1 command line parameter, but doing so is your own risk." << std::endl;

+            if(ignoreMaxBufferSize == 0)

+                return false;

         }

         int WorkGroupSizeLimitX, WorkGroupSizeLimitY, WorkGroupSizeLimitZ;

         glGetIntegeri_v(GL_MAX_COMPUTE_WORK_GROUP_COUNT,0,&WorkGroupSizeLimitX);

@@ -332,7 +334,8 @@ namespace Helpers
             {"--globalWorkgroupSizeZ", &globalWorkGroupSizeZ},

             {"--imageGamma",&pngGamma},

             {"--imageColorScale",&pngColorScale},

-            {"--output", &pngFilename}

+            {"--output", &pngFilename},

+            {"--ignoreMaxBufferSize", &ignoreMaxBufferSize}

         };

 

         for(int i=1; i < argc;++i)

@@ -358,7 +361,8 @@ namespace Helpers
                              "\tNOTE: There's also a limit on the product of the three local workgroup sizes, for which a number smaller or equal to 1024 is guaranteed to work. Higher numbers might work and run faster. Feel free to experiment." << std::endl <<

                              "--globalWorkgroupSizeX [integer] : How often the local work group should be invoked per frame. Values up to 65535 are guaranteed to work. Default is 1024." << std::endl <<

                              "--globalWorkgroupSizeY [integer] : How often the local work group should be invoked per frame. Values up to 65535 are guaranteed to work. Default is 1." << std::endl <<

-                             "--globalWorkgroupSizeZ [integer] : How often the local work group should be invoked per frame. Values up to 65535 are guaranteed to work. Default is 1." << std::endl;

+                             "--globalWorkgroupSizeZ [integer] : How often the local work group should be invoked per frame. Values up to 65535 are guaranteed to work. Default is 1." << std::endl <<

+                             "--ignoreMaxBufferSize [0,1] : If set to 1, a failed maximum buffer size check is not treated as error. Some graphics drivers report lower values than their absolute limit. Do this on your own risk, though." << std::endl;

                 return false;

             }

         }