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• ### Similar Content

• By elect
Hi,
ok, so, we are having problems with our current mirror reflection implementation.
At the moment we are doing it very simple, so for the i-th frame, we calculate the reflection vectors given the viewPoint and some predefined points on the mirror surface (position and normal).
Then, using the least squared algorithm, we find the point that has the minimum distance from all these reflections vectors. This is going to be our virtual viewPoint (with the right orientation).
After that, we render offscreen to a texture by setting the OpenGL camera on the virtual viewPoint.
And finally we use the rendered texture on the mirror surface.
So far this has always been fine, but now we are having some more strong constraints on accuracy.
What are our best options given that:
- we have a dynamic scene, the mirror and parts of the scene can change continuously from frame to frame
- we have about 3k points (with normals) per mirror, calculated offline using some cad program (such as Catia)
- all the mirror are always perfectly spherical (with different radius vertically and horizontally) and they are always convex
- a scene can have up to 10 mirror
- it should be fast enough also for vr (Htc Vive) on fastest gpus (only desktops)

Looking around, some papers talk about calculating some caustic surface derivation offline, but I don't know if this suits my case
Also, another paper, used some acceleration structures to detect the intersection between the reflection vectors and the scene, and then adjust the corresponding texture coordinate. This looks the most accurate but also very heavy from a computational point of view.

Other than that, I couldn't find anything updated/exhaustive around, can you help me?

• Hello all,
I am currently working on a game engine for use with my game development that I would like to be as flexible as possible.  As such the exact requirements for how things should work can't be nailed down to a specific implementation and I am looking for, at least now, a default good average case scenario design.
Here is what I have implemented:
Deferred rendering using OpenGL Arbitrary number of lights and shadow mapping Each rendered object, as defined by a set of geometry, textures, animation data, and a model matrix is rendered with its own draw call Skeletal animations implemented on the GPU.   Model matrix transformation implemented on the GPU Frustum and octree culling for optimization Here are my questions and concerns:
Doing the skeletal animation on the GPU, currently, requires doing the skinning for each object multiple times per frame: once for the initial geometry rendering and once for the shadow map rendering for each light for which it is not culled.  This seems very inefficient.  Is there a way to do skeletal animation on the GPU only once across these render calls? Without doing the model matrix transformation on the CPU, I fail to see how I can easily batch objects with the same textures and shaders in a single draw call without passing a ton of matrix data to the GPU (an array of model matrices then an index for each vertex into that array for transformation purposes?) If I do the matrix transformations on the CPU, It seems I can't really do the skinning on the GPU as the pre-transformed vertexes will wreck havoc with the calculations, so this seems not viable unless I am missing something Overall it seems like simplest solution is to just do all of the vertex manipulation on the CPU and pass the pre-transformed data to the GPU, using vertex shaders that do basically nothing.  This doesn't seem the most efficient use of the graphics hardware, but could potentially reduce the number of draw calls needed.

Really, I am looking for some advice on how to proceed with this, how something like this is typically handled.  Are the multiple draw calls and skinning calculations not a huge deal?  I would LIKE to save as much of the CPU's time per frame so it can be tasked with other things, as to keep CPU resources open to the implementation of the engine.  However, that becomes a moot point if the GPU becomes a bottleneck.

• Hello!
I would like to introduce Diligent Engine, a project that I've been recently working on. Diligent Engine is a light-weight cross-platform abstraction layer between the application and the platform-specific graphics API. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common front-end for all supported platforms and provides interoperability with underlying native API. Shader source code converter allows shaders authored in HLSL to be translated to GLSL and used on all platforms. Diligent Engine supports integration with Unity and is designed to be used as a graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. It is distributed under Apache 2.0 license and is free to use. Full source code is available for download on GitHub.
Features:
True cross-platform Exact same client code for all supported platforms and rendering backends No #if defined(_WIN32) ... #elif defined(LINUX) ... #elif defined(ANDROID) ... No #if defined(D3D11) ... #elif defined(D3D12) ... #elif defined(OPENGL) ... Exact same HLSL shaders run on all platforms and all backends Modular design Components are clearly separated logically and physically and can be used as needed Only take what you need for your project (do not want to keep samples and tutorials in your codebase? Simply remove Samples submodule. Only need core functionality? Use only Core submodule) No 15000 lines-of-code files Clear object-based interface No global states Key graphics features: Automatic shader resource binding designed to leverage the next-generation rendering APIs Multithreaded command buffer generation 50,000 draw calls at 300 fps with D3D12 backend Descriptor, memory and resource state management Modern c++ features to make code fast and reliable The following platforms and low-level APIs are currently supported:
Windows Desktop: Direct3D11, Direct3D12, OpenGL Universal Windows: Direct3D11, Direct3D12 Linux: OpenGL Android: OpenGLES MacOS: OpenGL iOS: OpenGLES API Basics
Initialization
The engine can perform initialization of the API or attach to already existing D3D11/D3D12 device or OpenGL/GLES context. For instance, the following code shows how the engine can be initialized in D3D12 mode:
#include "RenderDeviceFactoryD3D12.h" using namespace Diligent; // ...  GetEngineFactoryD3D12Type GetEngineFactoryD3D12 = nullptr; // Load the dll and import GetEngineFactoryD3D12() function LoadGraphicsEngineD3D12(GetEngineFactoryD3D12); auto *pFactoryD3D11 = GetEngineFactoryD3D12(); EngineD3D12Attribs EngD3D12Attribs; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[0] = 1024; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[1] = 32; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[2] = 16; EngD3D12Attribs.CPUDescriptorHeapAllocationSize[3] = 16; EngD3D12Attribs.NumCommandsToFlushCmdList = 64; RefCntAutoPtr<IRenderDevice> pRenderDevice; RefCntAutoPtr<IDeviceContext> pImmediateContext; SwapChainDesc SwapChainDesc; RefCntAutoPtr<ISwapChain> pSwapChain; pFactoryD3D11->CreateDeviceAndContextsD3D12( EngD3D12Attribs, &pRenderDevice, &pImmediateContext, 0 ); pFactoryD3D11->CreateSwapChainD3D12( pRenderDevice, pImmediateContext, SwapChainDesc, hWnd, &pSwapChain ); Creating Resources
Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. To create a buffer, you need to populate BufferDesc structure and call IRenderDevice::CreateBuffer(). The following code creates a uniform (constant) buffer:
BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); Similar, to create a texture, populate TextureDesc structure and call IRenderDevice::CreateTexture() as in the following example:
TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); Initializing Pipeline State
Diligent Engine follows Direct3D12 style to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.)
To create a shader, populate ShaderCreationAttribs structure. An important member is ShaderCreationAttribs::SourceLanguage. The following are valid values for this member:
SHADER_SOURCE_LANGUAGE_DEFAULT  - The shader source format matches the underlying graphics API: HLSL for D3D11 or D3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL  - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. See shader converter for details. SHADER_SOURCE_LANGUAGE_GLSL  - The shader source is in GLSL. There is currently no GLSL to HLSL converter. To allow grouping of resources based on the frequency of expected change, Diligent Engine introduces classification of shader variables:
Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. This post describes the resource binding model in Diligent Engine.
The following is an example of shader initialization:
To create a pipeline state object, define instance of PipelineStateDesc structure. The structure defines the pipeline specifics such as if the pipeline is a compute pipeline, number and format of render targets as well as depth-stencil format:
// This is a graphics pipeline PSODesc.IsComputePipeline = false; PSODesc.GraphicsPipeline.NumRenderTargets = 1; PSODesc.GraphicsPipeline.RTVFormats[0] = TEX_FORMAT_RGBA8_UNORM_SRGB; PSODesc.GraphicsPipeline.DSVFormat = TEX_FORMAT_D32_FLOAT; The structure also defines depth-stencil, rasterizer, blend state, input layout and other parameters. For instance, rasterizer state can be defined as in the code snippet below:
// Init rasterizer state RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; //RSDesc.MultisampleEnable = false; // do not allow msaa (fonts would be degraded) RasterizerDesc.AntialiasedLineEnable = False; When all fields are populated, call IRenderDevice::CreatePipelineState() to create the PSO:
Shader resource binding in Diligent Engine is based on grouping variables in 3 different groups (static, mutable and dynamic). Static variables are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. They are bound directly to the shader object:

m_pPSO->CreateShaderResourceBinding(&m_pSRB); Dynamic and mutable resources are then bound through SRB object:
m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "tex2DDiffuse")->Set(pDiffuseTexSRV); m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); The difference between mutable and dynamic resources is that mutable ones can only be set once for every instance of a shader resource binding. Dynamic resources can be set multiple times. It is important to properly set the variable type as this may affect performance. Static variables are generally most efficient, followed by mutable. Dynamic variables are most expensive from performance point of view. This post explains shader resource binding in more details.
Setting the Pipeline State and Invoking Draw Command
Before any draw command can be invoked, all required vertex and index buffers as well as the pipeline state should be bound to the device context:
// Clear render target const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); m_pContext->SetPipelineState(m_pPSO); Also, all shader resources must be committed to the device context:
m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); When all required states and resources are bound, IDeviceContext::Draw() can be used to execute draw command or IDeviceContext::DispatchCompute() can be used to execute compute command. Note that for a draw command, graphics pipeline must be bound, and for dispatch command, compute pipeline must be bound. Draw() takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); Tutorials and Samples
The GitHub repository contains a number of tutorials and sample applications that demonstrate the API usage.

AntTweakBar sample demonstrates how to use AntTweakBar library to create simple user interface.

Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to textures, using compute shaders and unordered access views, etc.

The repository includes Asteroids performance benchmark based on this demo developed by Intel. It renders 50,000 unique textured asteroids and lets compare performance of D3D11 and D3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

Integration with Unity
Diligent Engine supports integration with Unity through Unity low-level native plugin interface. The engine relies on Native API Interoperability to attach to the graphics API initialized by Unity. After Diligent Engine device and context are created, they can be used us usual to create resources and issue rendering commands. GhostCubePlugin shows an example how Diligent Engine can be used to render a ghost cube only visible as a reflection in a mirror.

• By Yxjmir
I'm trying to load data from a .gltf file into a struct to use to load a .bin file. I don't think there is a problem with how the vertex positions are loaded, but with the indices. This is what I get when drawing with glDrawArrays(GL_LINES, ...):

Also, using glDrawElements gives a similar result. Since it looks like its drawing triangles using the wrong vertices for each face, I'm assuming it needs an index buffer/element buffer. (I'm not sure why there is a line going through part of it, it doesn't look like it belongs to a side, re-exported it without texture coordinates checked, and its not there)
I'm using jsoncpp to load the GLTF file, its format is based on JSON. Here is the gltf struct I'm using, and how I parse the file:
glBindVertexArray(g_pGame->m_VAO);
glDrawElements(GL_LINES, g_pGame->m_indices.size(), GL_UNSIGNED_BYTE, (void*)0); // Only shows with GL_UNSIGNED_BYTE
glDrawArrays(GL_LINES, 0, g_pGame->m_vertexCount);
So, I'm asking what type should I use for the indices? it doesn't seem to be unsigned short, which is what I selected with the Khronos Group Exporter for blender. Also, am I reading part or all of the .bin file wrong?
Test.gltf
Test.bin

• That means how do I use base DirectX or OpenGL api's to make a physics based destruction simulation?
Will it be just smart rendering or something else is required?

# OpenGL AMD 6310 GLSL/FBO texture copy issue

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I'm using OpenGL 2.0 and an FBO to copy some data from an RGBA texture to an RGB texture, and I ran into an issue where sometimes it "corrupts" the first few lowest order bits of some of the pixel components during the copy.

The texture copy is broken up into several steps, and I'm resizing the FBO.

At first I thought perhaps it was a problem related to the way that I was resizing the FBO, or with the way the the texture is being sampled, but the problem doesn't always occur, and when it does, it never occurs for every pixel copied nor does it ever occur for all of the components of each problematic pixel. In other words, it seems nearly random, except that it is indeed deterministic insomuch that the same error(s) occur if the same input float values are used during each run of the program.

Also, the problem never, ever occurs if I always use an FBO size of 1x1 (which is kind of misleading to know, because it made me think that it was a sampling issue, but, again, that is probably not the case since not every component of every problematic pixel is "corrupted"). Unfortunately, using an FBO size of 1x1 is absolutely useless in the real world where I'm going to be copying a texture containing anything more than a few pixels.

The problem happens on Windows 7 and Ubuntu, and the problem happens when I use MSVC++ or g++'s std rand() or Mersenne Twister to generate the input texture values (not that how I generate the values should matter, since copy operations are by definition independent of how the data to be copied was generated beforehand) .

I wrote a test program (see code below) where nothing changes between runs of the program other than the input texture values.

Does anyone have an AMD 6310 (or any other kind of hardware, really) that they can run this test program on? You'll have to run it a few times, as sometimes it produces an error, and sometimes it does not. I'm just curious if it ever produces the error on your hardware. I just can't spot the pattern, and my naive thinking is that this should either work all of the time, or never -- not so sporadically.

I'm also totally wiling to accept that it might, in the end, have something to do with the way that I'm using OpenGL to do the copy. This would be relieving actually, since it would mean that there's an easy and reliable solution. I hope this is the case.

I probably have some extraneous calls to glTexParameteri in there somewhere, but I was trying the "better safe than sorry" method while working on this test program.

In any case, the problem results in some of the pixel components having error that's on the order of like ~1e-8. Yes, that's a very small error, but it's totally unacceptable for what I'm doing.

#include <iostream>
using std::cout;
using std::endl;

#include <iomanip>
using std::ios_base;
using std::setprecision;
using std::fixed;

#include <vector>
using std::vector;

#include <string>
using std::string;

#include <utility>
using std::pair;

#include <cmath>
#include <cstdlib> // MSVC++ chokes if you don't include this before glut.h
#include <ctime>

#include <GL/glew.h>
#include <GL/glut.h>

// Automatically link in the GLUT and GLEW libraries if compiling on MSVC++
#ifdef _MSC_VER
#pragma comment(lib, "glew32")
#pragma comment(lib, "glut32")
#endif

float dist(float a, float b);
void get_chunk_sizes(const size_t num_pixels, vector< pair<size_t, size_t> > &chunk_sizes, const bool force_1x1_chunks, const bool force_square_chunks = false);
string float_bits_string(const float f);

int main(int argc, char **argv)
{
// This program uses an FBO and a fragment shader to copy RGBA pixels from an input array into an RGB output array.
// It breaks up the entire pixel copy process into many smaller chunks of a varying number of pixels per chunk.
// See line 165 to change the number of pixels in the array (right now it's hard-coded to be 7 pixels total).

// If the chunk sizes are forced to be 1x1 pixels, then there are never any problems with the copy.
// See line 186 to change whether the chunks are forced to be 1x1 pixels or not (right not they are not being forced as such).
//
// If the chunk sizes are not forced to be 1x1 pixels, then almost all of the time (but not quite always)
// there is a small problem with at least one component of one of the pixels during the copy:
//
// The copy is off by a small, non-zero value of practically constant magnitude (on the order of ~1e-8).
//
// Since the values of the pixel components are the only thing that change between runs of the program,
// the problem seems to be entirely dependent on the values of the pixel components themselves. This is totally
// unexpected -- it should always work or always fail to the same degree, regardless of the pixel component values.
// While looking at the bit patterns of the problematic pixel component values, it seems that it is always only the
// first three to five lowest order bits that do not get copied successfully.
//
// Note that if the values of the pixel components do not change between runs, then the same errors occur,
// and so the problem seems to be entirely deterministic. Right now the components are set via PRNG, and are done in a way
// so that all of the bits of precision are used (see lines 173 - 176).
// See line 86 to alter the PRNG seed.

// 1) Initialize pseudo-random number generator.
srand(time(0)); // srand(0);

// 2) Initialize OpenGL and related objects.
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA);
GLint glut_window_handle = glutCreateWindow("");

if(! ( GLEW_OK == glewInit() &&
GLEW_VERSION_2_0 &&
GLEW_ARB_framebuffer_object &&
GLEW_ARB_texture_rectangle ) )
{
return -1;
}

GLuint fbo_handle = 0;
GLuint tex_fbo_handle = 0;
GLuint tex_in_handle = 0;
GLuint tex_out_handle = 0;
const GLint tex_in_internal_format = GL_RGBA32F_ARB;
const GLint tex_in_format = GL_RGBA;
const GLint tex_out_internal_format = GL_RGB32F_ARB;
const GLint tex_out_format = GL_RGB;
const GLint var_type = GL_FLOAT;

string code;
code += "#version 110\n";
code += "uniform sampler2D input_tex;\n";
code += "void main(void)\n";
code += "{\n";
code += "    vec4 p = texture2D(input_tex, gl_TexCoord[0].st);\n";
code += "    gl_FragData[0].rgb = vec3(p.xyz);\n";
code += "}\n";

string error;

{
cout << error << endl;
return -2;
}

glGenTextures(1, &tex_in_handle);
glBindTexture(GL_TEXTURE_2D, tex_in_handle);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glGenTextures(1, &tex_out_handle);
glBindTexture(GL_TEXTURE_2D, tex_out_handle);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glGenFramebuffersEXT(1, &fbo_handle);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo_handle);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glGenTextures(1, &tex_fbo_handle);
glBindTexture(GL_TEXTURE_2D, tex_fbo_handle);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glUniform1i(glGetUniformLocation(shader_handle, "input_tex"), 0); // Use texture 0.

// 3) Set up input -- an array of RGBA float pixels with pseudorandom values.
size_t num_pixels = 7; // = rand() % 50 + 1;
size_t num_input_channels = 4;
vector<float> input(num_pixels*num_input_channels, 0);

for(size_t i = 0; i < num_pixels; i++)
{
size_t input_index = i*num_input_channels;

input[input_index + 0] = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
input[input_index + 1] = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
input[input_index + 2] = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
input[input_index + 3] = static_cast<float>(rand()) / static_cast<float>(RAND_MAX);
}

// 4) Break up processing of input into chunks.
vector< pair<size_t, size_t> > chunks;

#ifdef FORCE_1x1_CHUNKS
get_chunk_sizes(num_pixels, chunks, true, true);
#else
get_chunk_sizes(num_pixels, chunks, false, true);
#endif

size_t num_pixels_remaining = num_pixels;

size_t num_output_channels = 3;
vector<float> output(num_pixels*num_output_channels, 0);

for(size_t i = 0; i < chunks.size(); i++)
{
cout << "Pixels remaining: " << num_pixels_remaining << ", processing chunk size: " << chunks.first << " x " << chunks.second << " = " << chunks.first*chunks.second << endl;

const size_t tex_size_x = chunks.first;
const size_t tex_size_y = chunks.second;
const size_t index = num_pixels - num_pixels_remaining;
const size_t input_index = index*num_input_channels;
const size_t output_index = index*num_output_channels;

// Set the FBO size to match the current chunk size.
glBindTexture(GL_TEXTURE_2D, tex_fbo_handle);
glTexImage2D(GL_TEXTURE_2D, 0, tex_out_internal_format, tex_size_x, tex_size_y, 0, tex_out_format, var_type, 0);
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, tex_fbo_handle, 0);

// Write to GPU memory.
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex_in_handle);
glTexImage2D(GL_TEXTURE_2D, 0, tex_in_internal_format, tex_size_x, tex_size_y, 0, tex_in_format, var_type, &input[input_index]);

// Calculate by "drawing".
glMatrixMode(GL_PROJECTION);
glOrtho(0, 1, 0, 1, 0, 1);
glMatrixMode(GL_MODELVIEW);
glViewport(0, 0, tex_size_x, tex_size_y);

glTexCoord2f(0, 1);    glVertex2f(0, 1);
glTexCoord2f(0, 0);    glVertex2f(0, 0);
glTexCoord2f(1, 0); glVertex2f(1, 0);
glTexCoord2f(1, 1);    glVertex2f(1, 1);
glEnd();

glReadPixels(0, 0, tex_size_x, tex_size_y, tex_out_format, var_type, &output[output_index]);

num_pixels_remaining -= tex_size_x*tex_size_y;
}

// 5) Analyze largest distance between input and output -- it should be zero, but it is not zero
//    if the chunk sizes are not forced to be 1x1.
float largest_dist = 0;
cout << setprecision(18);

cout << endl << "Comparing input and output: " << endl;

for(size_t i = 0; i < num_pixels; i++)
{
size_t input_index = i*num_input_channels;
size_t output_index = i*num_output_channels;

float dist0 = dist(input[input_index + 0], output[output_index + 0]);
float dist1 = dist(input[input_index + 1], output[output_index + 1]);
float dist2 = dist(input[input_index + 2], output[output_index + 2]);

if(dist0 > largest_dist)
largest_dist = dist0;

if(dist1 > largest_dist)
largest_dist = dist1;

if(dist2 > largest_dist)
largest_dist = dist2;

if(dist0 != 0)
{
cout << endl;
cout << "**** Copy error at pixel " << i + 1  << " first component" << endl;
cout << "\tInput:  " << input[input_index + 0] << '\n' << "\tOutput: " << output[output_index + 0] << endl;
cout << "\tInput (as bits):  " << float_bits_string(input[input_index + 0]) << '\n' << "\tOutput (as bits): " << float_bits_string(output[output_index + 0]) << endl;
cout << endl;
}
else
{
cout << "OK at pixel " << i + 1  << " first component" << endl;
//            cout << "\tInput:  " << input[input_index + 0] << '\n' << "\tOutput: " << output[output_index + 0] << endl;
}

if(dist1 != 0)
{
cout << endl;
cout << "**** Copy error at pixel " << i + 1 << " second component" << endl;
cout << "\tInput:  " << input[input_index + 1] << '\n' << "\tOutput: " << output[output_index + 1] << endl;
cout << "\tInput (as bits):  " << float_bits_string(input[input_index + 1]) << '\n' << "\tOutput (as bits): " << float_bits_string(output[output_index + 1]) << endl;
cout << endl;
}
else
{
cout << "OK at pixel " << i + 1 << " second component" << endl;
//            cout << "\tInput:  " << input[input_index + 1] << '\n' << "\tOutput: " << output[output_index + 1] << endl;
}

if(dist2 != 0)
{
cout << endl;
cout << "**** Copy error at pixel " << i + 1 << " third component" << endl;
cout << "\tInput:  " << input[input_index + 2] << '\n' << "\tOutput: " << output[output_index + 2] << endl;
cout << "\tInput (as bits):  " << float_bits_string(input[input_index + 2]) << '\n' << "\tOutput (as bits): " << float_bits_string(output[output_index + 2]) << endl;
cout << endl;
}
else
{
cout << "OK at pixel " << i + 1 << " third component" << endl;
//            cout << "\tInput:  " << input[input_index + 2] << '\n' << "\tOutput: " << output[output_index + 2] << endl;
}

}

if(0 != largest_dist)
cout << "\nLargest copy error: " << largest_dist << endl;
else
cout << "\nNo copy errors." << endl;

// 6) Cleanup OpenGL and related objects.
glDeleteTextures(1, &tex_in_handle);
glDeleteTextures(1, &tex_out_handle);
glDeleteTextures(1, &tex_fbo_handle);
glDeleteFramebuffersEXT(1, &fbo_handle);
glUseProgram(0);
glutDestroyWindow(glut_window_handle);

return 0;
}

float dist(float a, float b)
{
return fabsf(b - a);
}

{
error = "";

const char *cch = 0;
GLint status = GL_FALSE;

if(GL_FALSE == status)
{
error = "Fragment shader compile error.\n";
vector<GLchar> buf(4096, '\0');

for(size_t i = 0; i < buf.size(); i++)
if(0 != buf)
error += buf;

error += '\n';

return false;
}

if(GL_FALSE == status)
{
vector<GLchar> buf(4096, '\0');

for(size_t i = 0; i < buf.size(); i++)
if(0 != buf)
error += buf;

error += '\n';

return false;
}

// Cleanup.

return true;
}

void get_chunk_sizes(const size_t num_pixels, vector< pair<size_t, size_t> > &chunk_sizes, const bool force_1x1_chunks, const bool force_square_chunks)
{
chunk_sizes.clear();

size_t num_pixels_remaining = num_pixels;
GLint max_tex_size = 0;

glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max_tex_size);

size_t curr_tex_x = max_tex_size;
size_t curr_tex_y = max_tex_size;

if(true == force_1x1_chunks)
curr_tex_x = curr_tex_y = 1;

while(0 < num_pixels_remaining)
{
if(num_pixels_remaining < curr_tex_x*curr_tex_y)
{
if(true == force_square_chunks)
{
curr_tex_x /= 2;
curr_tex_y /= 2;
}
else
{
if(curr_tex_x == curr_tex_y)
curr_tex_y /= 2;
else
curr_tex_x /= 2;
}
}
else
{
pair<size_t, size_t> p(curr_tex_x, curr_tex_y);
chunk_sizes.push_back(p);
num_pixels_remaining -= curr_tex_x*curr_tex_y;
}
}
}

string float_bits_string(const float f)
{
long unsigned int bit_mask = 1;
long unsigned int intval = *(long unsigned int*)&f;

string bits;

for(size_t i = 0; i < 32; i++, bit_mask <<= 1)
{
bits += '1';
else
bits += '0';
}

bits = string(bits.rbegin(), bits.rend());

return bits;
}


Edited by taby