View Full Version : glMapBufferRange doesn't set the value of of compute shader array

02-27-2014, 07:20 AM
Hi everyone, new poster here. I've been trying to implement tiled deferred shading and I've been stuck on a problem for some time now. I'm trying to store an array of structs consisting of point lights that I want to initalize and send to a compute shader where I can process it further. I'm using a Shader Storage Buffer Object for this and I'm trying to use glMapBufferRange to provide the values. I've added some checks so that if the array size is 0 I'll paint the screen red and if it's larger than 0 it's yellow, so far I can't seem to get it to work.

Here's the compute shader:

#version 430
#define SCREEN_WIDTH 1280.0f
#define SCREEN_HEIGHT 720.0f

uniform sampler2D positionMap;
uniform sampler2D colorMap;
uniform sampler2D normalMap;
uniform sampler2D depthMap;

layout(binding = 4, rgba32f) uniform writeonly image2D finalImage;
layout(binding = 5, rgba32f) uniform writeonly image2D otherImage;

struct PointLight
vec3 position; //4,8,12
vec3 color; // 16,20, 24
float radius; //28
float diffuseIntensity; //32
float ambientIntensity; //36
float Constant; //40
float Linear; //44
float Exp; //48

layout(std430, binding = 6) buffer BufferObject
PointLight pointLights[];

shared uint minDepth;
shared uint maxDepth;

layout(local_size_x = MAX_WORK_GROUP_SIZE, local_size_y = MAX_WORK_GROUP_SIZE)in;

void main()

if(gl_LocalInvocationIndex == 0){
minDepth = 0xFFFFFFFF;
maxDepth = 0;
ivec2 pixelPos = ivec2(gl_GlobalInvocationID.xy);
vec2 uv = vec2(pixelPos.x / SCREEN_WIDTH, pixelPos.y / SCREEN_HEIGHT);

float d = texture(depthMap,uv).z;

uint depth = uint(d * 0xFFFFFFFF);

//compares the content of minDepth to depth and writes the minimum value to minDepth
atomicMin(minDepth, depth);
// barrier();
//compares the content of maxDepth to depth and writes the maximum value to the maxDepth
atomicMax(maxDepth, depth);

///Write a single texel into an image
/* barrier();
imageStore(finalImage, pixelPos, vec4(float(float(maxDepth) / float(0xFFFFFFFF))));

imageStore(otherImage, pixelPos, vec4(float(float(minDepth) / float(0xFFFFFFFF))));

PointLight p = pointLights[0];
PointLight p2 = pointLights[1];
if(pointLights.length() == 0)
imageStore(finalImage, pixelPos, vec4(1.0,0.0,0.0,1.0));

imageStore(otherImage, pixelPos, vec4(1.0,0.0,0.0,1.0));
if(pointLights.length() > 0)
imageStore(finalImage, pixelPos, vec4(1.0,1.0,0.0,1.0));

imageStore(otherImage, pixelPos, vec4(1.0,1.0,0.0,1.0));


Here's how I'm trying to initalize the buffer with some test values:

My3dVector currentColor(1.0f,1.0f,1.0f);
glBindBuffer(GL_SHADER_STORAGE_BUFFER,m_pointLight Buffer);

struct TDPointLight* pointlights = (struct TDPointLight*) glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0, NUM_OF_LIGHTS*sizeof(struct TDPointLight), GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_BUFFER_BIT );

int shit = ARRAY_SIZE_IN_ELEMENTS(pointlights);
for(int i = 0; i < NUM_OF_LIGHTS; ++i)
float Max = 80.0f;
float Min = -80.0f;

float MaxZ = 80.0f;
float MinZ = -80.0f;

float ranx = ((float(rand()) / float(RAND_MAX)) * (Max - Min)) + Min;
float ranz = ((float(rand()) / float(RAND_MAX)) * (Max - Min)) + Min;

int maxCol = 8;
int minCol = 1;
//int ranCol = ((rand() / RAND_MAX) * (maxCol - minCol)) + minCol;
int ranCol = (rand()%(maxCol-minCol))+minCol;

if(ranCol == 0)
printf("error, color 8 doesnt exist");
if(ranCol == 1)
currentColor = COLOR_WHITE;
if(ranCol == 2)
currentColor = COLOR_RED;
if(ranCol == 3)
currentColor = COLOR_GREEN;
if(ranCol == 4)
currentColor = COLOR_CYAN;
if(ranCol == 5)
currentColor = COLOR_BLUE;
if(ranCol == 6)
currentColor = COLOR_PURPLE;
if(ranCol == 7)
currentColor = COLOR_ORANGE;
if(ranCol == 8)
printf("error, color 8 doesnt exist");

pointlights[i].position = My3dVector(1.0f,1.0f,1.0f);
pointlights[i].color = My3dVector(1.0f,0.0f,0.0f);
pointlights[i].radius = 10.0f;
pointlights[i].diffuseIntensity = 10.0f;
pointlights[i].ambientIntensity = 0.1f;
//pointlights[i].color = currentColor;
//pointlights[i].position = My3dVector(ranx,3.0f,ranz);
//m_pointLight[i].m_Position = My3dVector(0.0f,2.0f,0.0f);
pointlights[i].Constant = 0.0f;
pointlights[i].Linear = 0.0f;
pointlights[i].Exp = 0.6f;

Then the process goes something like:

1. Use the compute shader
2. Set all the uniforms, then bind some deferred textures and other things using this code

for(unsigned int i = 0; i<ARRAY_SIZE_IN_ELEMENTS(m_textures); ++i)
glActiveTexture(GL_TEXTURE0 + i);
glBindTexture(GL_TEXTURE_2D, m_textures[TDGBuffer_TEXTURE_TYPE_POSITION + i]);

glBindImageTexture(4, m_finalTexture, 0, GL_FALSE, 0, GL_WRITE_ONLY, GL_RGBA32F);

glBindImageTexture(5,m_otherTexture,0,GL_FALSE,0,G L_WRITE_ONLY,GL_RGBA32F);

glBindBufferBase(GL_SHADER_STORAGE_BUFFER,6,m_poin tLightBuffer);

Then finally in the main loop call these functions

glDispatchCompute((window_width/MAX_WORK_GROUP_SIZE), (window_height/MAX_WORK_GROUP_SIZE), 1);

It doesn't work with any memory barriers anywhere in the code, but as I'm not modifying the contents anywhere this shouldn't be a problem as it just gets initialized once and then remains the same forever.

02-27-2014, 03:33 PM
A couple of things to look at

1) I have had trouble with std430 on AMD cards not packing correctly

2) avoid using vec3 in your structures; use vec4 and put one of your extra variables in the spare float.

02-28-2014, 12:34 AM
Thanks for the response. I tried rearranging the structures it didn't appear to help. I'm also running a nvidia card. I'm really confused about what's happening since I call the glmapbufferrange after I have created and used the compute shader, so it should recieve the data.

02-28-2014, 01:41 AM
Okay I think I have found a solution, after rearranging the structures so they look like this

struct PointLight
vec4 position; //4,8,12
//float radius; //28
vec4 color; // 16,20, 24

float diffuseIntensity; //32
//float ambientIntensity; //36
float Constant; //40
float Linear; //44
float Exp; //48


struct TDPointLight
My3dVector position; //4,8,12
float radius; //28
My3dVector color; // 16,20, 24
float ambientIntensity; //36
float diffuseIntensity; //32

float Constant; //40
float Linear; //44
float Exp; //48

I can now print out the correct color to the framebuffer using:

PointLight p = pointLights[3];
PointLight p2 = pointLights[55];

//vec3 test = vec3(p.posX,p.posY,p.posZ);
//vec3 test2 = vec3(p2.posX,p2.posY,p2.posZ);
vec4 test = p.color;
vec4 test2 = p2.color;

imageStore(finalImage, pixelPos, test);

imageStore(otherImage, pixelPos, test2);

Which appears to be working just fine, I think I'll just add some extra floats that are constantly 1 for the w value of the vec4. I think the problem is that the length function either doesn't work as I thought it did or I've done something horribly wrong. I still get a length size of 0 for it, which I think is because it didn't update the length of the array when it gets set by a buffer, which seems logical.

02-28-2014, 04:49 PM
You might want to read the memory layout section on this page (http://www.opengl.org/wiki/Interface_Block_(GLSL)). I always use std140 which is very specifiy about the layout.