First-Time GLSL Shadow Mapping Problems
- by Locke
I'm working on building out a 2.5D engine and having massive problems getting my shadows working. I'm at a point where I'm VERY close.
So, let's see a picture to see what I have:
As you can see above, the image has lighting -- but the shadow map is displaying incorrectly. The shadow map is shown in the bottom left hand side of the screen as a normal 2D texture, so we can see what it looks like at any given time.
If you notice, it appears that the shadows are generating backwards in the wrong direction -- I think. But the problem is a little more deep -- I'm just plotting the shadow onto the screen, which I know is wrong -- I'm ignoring the actual test to see if we NEED to show a shadow.
The incoming parameters all appear to be correct -- so there has to be something wrong with my shader code somewhere.
Here's what my code looks like:
VERTEX:
uniform mat4 LightModelViewProjectionMatrix;
varying vec3 Normal; // The eye-space normal of the current vertex.
varying vec4 LightCoordinate; // The texture coordinate of the light of the current vertex.
varying vec3 LightDirection; // The eye-space direction of the light.
void main()
{
Normal = normalize(gl_NormalMatrix * gl_Normal);
LightDirection = normalize(gl_NormalMatrix * gl_LightSource[0].position.xyz);
LightCoordinate = LightModelViewProjectionMatrix * gl_Vertex;
LightCoordinate.xy = ( LightCoordinate.xy * 0.5 ) + 0.5;
gl_Position = ftransform();
gl_TexCoord[0] = gl_MultiTexCoord0;
}
FRAGMENT:
uniform sampler2D DiffuseMap;
uniform sampler2D ShadowMap;
varying vec3 Normal; // The eye-space normal of the current vertex.
varying vec4 LightCoordinate; // The texture coordinate of the light of the current vertex.
varying vec3 LightDirection; // The eye-space direction of the light.
void main()
{
vec4 Texel = texture2D(DiffuseMap, vec2(gl_TexCoord[0]));
// Directional lighting
//Build ambient lighting
vec4 AmbientElement = gl_LightSource[0].ambient;
//Build diffuse lighting
float Lambert = max(dot(Normal, LightDirection), 0.0); //max(abs(dot(Normal, LightDirection)), 0.0);
vec4 DiffuseElement = ( gl_LightSource[0].diffuse * Lambert );
vec4 LightingColor = ( DiffuseElement + AmbientElement );
LightingColor.r = min(LightingColor.r, 1.0);
LightingColor.g = min(LightingColor.g, 1.0);
LightingColor.b = min(LightingColor.b, 1.0);
LightingColor.a = min(LightingColor.a, 1.0);
LightingColor *= Texel;
//Everything up to this point is PERFECT
// Shadow mapping
// ------------------------------
vec4 ShadowCoordinate = LightCoordinate / LightCoordinate.w;
float DistanceFromLight = texture2D( ShadowMap, ShadowCoordinate.st ).z;
float DepthBias = 0.001;
float ShadowFactor = 1.0;
if( LightCoordinate.w > 0.0 )
{
ShadowFactor = DistanceFromLight < ( ShadowCoordinate.z + DepthBias ) ? 0.5 : 1.0;
}
LightingColor.rgb *= ShadowFactor;
//gl_FragColor = LightingColor;
//Yes, I know this is wrong, but the line above (gl_FragColor = LightingColor;) produces the wrong effect
gl_FragColor = LightingColor * texture2D( ShadowMap, ShadowCoordinate.st );
}
I wanted to make sure the coordinates were correct for the shadow map -- so that's why you see it applied to the image as it is below. But the depth for each point seems to be wrong -- the shadows SHOULD be opposite (look at how the image is -- the shaded areas from normal lighting are facing the opposite direction of the shadows).
Maybe my matrices are bad or something going in? They're isolated and appear to be correct -- nothing else is going in unusual. When I view from the light's view and get the MVP matrices for it, they're correct.
EDIT: Added an image so you can see what happens when I do the correct command at the end of the GLSL:
That's the image when the last line is just glFragColor = LightingColor;
Maybe someone has some idea of what I screwed up?
