Problems with using a shadow map with deferred rendering Opengl 3.3

Question

I am trying to implement simple shadow mapping for a project i am working on. I can render the depth texture to the screen so i know it's there, the problem is when I sample the shadow map with the shadow texture coordinates it seems as if the coordinates are off.

Here is my light space matrix calculation

mat4x4 lightViewMatrix;

vec3 sun_pos = {SUN_OFFSET  * the_sun->direction[0],
                SUN_OFFSET  * the_sun->direction[1],
                SUN_OFFSET  * the_sun->direction[2]};

mat4x4_look_at(lightViewMatrix,sun_pos,player->pos,up);

mat4x4_mul(lightSpaceMatrix,lightProjMatrix,lightViewMatrix);

I will tweak the values for the size and frustum of the shadow map, but for now i just want to draw shadows around the player position

the_sun->direction is a normalized vector so i multiply it by a constant to get the position.

player->pos is the camera position in world space

the light projection matrix is calculated like this:

 mat4x4_ortho(lightProjMatrix,-SHADOW_FAR,SHADOW_FAR,-SHADOW_FAR,SHADOW_FAR,NEAR,SHADOW_FAR);

Shadow vertex shader:

uniform mat4 light_space_matrix;

 void main()
 {
     gl_Position = light_space_matrix * transfMatrix * vec4(position, 1.0f); 
 }

Shadow fragment shader:

out float fragDepth;
void main()
{
    fragDepth = gl_FragCoord.z;
}

I am using deferred rendering so i have all my world positions in the g_positions buffer

My shadow calculation in the deferred fragment shader:

float get_shadow_fac(vec4 light_space_pos)
{
    vec3 shadow_coords = light_space_pos.xyz / light_space_pos.w;
    shadow_coords      = shadow_coords * 0.5 + 0.5;

    float closest_depth = texture(shadow_map, shadow_coords.xy).r;
    float current_depth = shadow_coords.z;

    float shadow_fac = 1.0;

    if(closest_depth < current_depth)
       shadow_fac   = 0.5;

    return shadow_fac;
 }

I call the function like this:

get_shadow_fac(light_space_matrix * vec4(position,1.0));

Where position is the value i got from sampling the g_position buffer

Here is my depth texture (i know it will produce low quality shadows but i just want to get it working for now):

sorry because of the compression , the black smudges are trees ... https://i.stack.imgur.com/T43aK.jpg

EDIT: Depth texture attachment:

glTexImage2D(GL_TEXTURE_2D, 0,GL_DEPTH_COMPONENT24,fbo->width,fbo->height,0,GL_DEPTH_COMPONENT,GL_FLOAT,NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, fbo->depthTexture, 0);

Gicla Gicla · Accepted Answer · 2018-01-06T17:51:10

I found out what the problem was , my g_positions buffers texture had the internal format of GL_RGBA8 and that is too small to hold positions in world space

glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA8,fbo->width,fbo->height,0,GL_RGBA,GL_UNSIGNED_BYTE,NULL);

so when i changed to

glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA32F,fbo->width,fbo->height,0,GL_RGB,GL_FLOAT,NULL);

shadows appeared :D

Problems with using a shadow map with deferred rendering Opengl 3.3

1 Answers