I'm trying to render shadow using shadow mapping. But something is wrong. I think my shader could be wrongly written.
What I've tried to do is the following.
Generate the framebuffer for shadow map.
GLuint framebuffer;
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
GLuint shadow;
glGenTextures(1, &shadow);
glBindTexture(GL_TEXTURE_2D, shadow);
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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT ,
1366, 768,
0, GL_DEPTH_COMPONENT, GL_FLOAT,
0);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, shadow, 0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT,
1366, 768,
0, GL_DEPTH_COMPONENT, GL_FLOAT,
NULL);shadow, 0);
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
cout << "framebuffer error" << endl;
else
cout << "framebuffer is complete" << endl;
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glBindRenderbuffer(GL_RENDERBUFFER, 0);
Use two shader programs. The first is used to render into the depth texture of the framebuffer. The second is used for normal rendering and shadow.
The first shader program is like this.
///////////
first.program.vs
#version 330
in vec3 position;
uniform mat4 mM;
uniform mat4 mV;
uniform mat4 mP;
void main(){ gl_Position = mP * mV * mM * vec4(position, 1.0);
///////////////
first.program.fs
out vec4 fcolor;
void main() { fcolor = vec4(gl_FragCoord.z);
the second shader program is like the following.
//////////
second.program.vs
#version 330
in vec3 position;
in vec2 UV;
out vec2 uv;
// Matrix to get vertex position to clip space
uniform mat4 mM;
uniform mat4 mV;
uniform mat4 mP;
// Proj-View-Model matrix for Light
uniform mat4 mvp;
out vec4 ShadowCoord;
uniform vec3 lightPos;
out float dis;
void main(){ uv = UV;
ShadowCoord = mvp * vec4(position,1.0f);
gl_Position = mP * mV * mM * vec4(position, 1.0); }
//////
second.program.fs
#version 330
uniform sampler2D tex;
uniform sampler2D shadtex;
in vec2 uv; in vec3 normal;
in vec4 ShadowCoord;
out vec3 fcolor;
void main() {
fcolor = ( (texture(tex,uv).rgb));
float shadow = 1.0;
vec4 shadowcoord = (ShadowCoord / ShadowCoord.w);
shadowcoord = 0.5 * shadowcoord + 0.5;
if ((shadowcoord.x < 0 || shadowcoord.x > 1 || shadowcoord.y < 0 || shadowcoord.y > 1 || shadowcoord.z < 0 || shadowcoord.z > 1)){ shadow = 1.0; }
else { float depth = texture2D(shadtex, vec2(shadowcoord.xy)).x; if ( dis > depth ) shadow = 0;} fcolor *= shadow; }";
///////
in the main loop i draw objects in this way:
1. bind framebuffer
2. use first shader program
3. draw the object that cast shadow
4 bind the default framebuffer
5. use second shader program
6. draw the objects that have the shadow casted on them
But the result is not as expected. Is there something wrong in the second program's shaders? Thanks in advance.
In the picture the red box is the light position. The little screen in upper right is what rendered into the framebuffer, what
light sees.The blue plane in front of it is the shadow caster. I only rendered itto the shadow map framebuffer. I rendered the same blue plane in the exact position of the shadow caster, and ground beneath it. The shadow should be in front of the blue plane, not behind it. Also some online tutorial pointed out that glDrawBuffer(GL_NONE) means opengl will not draw to the color texture of the framebuffer, or similar meaning. So I wrote that.
