Instead of explicitly setting uniform data for a GL program, I set 'defaults' in a simple test (fragment) shader with:
uniform vec3 face_rgb[] = vec3[]
(
vec3(0.0, 0.0, 1.0), vec3(0.0, 1.0, 0.0), vec3(1.0, 0.0, 0.0),
vec3(1.0, 0.0, 1.0), vec3(0.0, 1.0, 1.0), vec3(1.0, 1.0, 0.0),
vec3(0.2, 0.2, 0.2), vec3(0.0, 0.0, 0.0)
);
Depending on the fragment's texture coordinates, an index value is formulated to look up an RGB value. (The actual RGB values are immaterial)
This works perfectly well with OS X (GL 3.2 core profile). In fact, far better than using an index with a const array. My question is - is this valid GLSL syntax, and not an implementation-dependent hack? (I have no 4+ access at the moment, but I assume the answer still applies). Also, any ideas as to why a uniform might outperform a constant array?
Yes, uniform arrays are allowed to have default values in GL 3.2. So your syntax is valid.
That doesn't mean it will always work, only that it's valid. Driver bugs can still get you.
Related
I am currently trying to apply a normal map in my shader but the shading in the final image is way off.
Surfaces that should be shaded are completely bright, surfaces that should be bright are completely shaded and the top surface, which should have the same shade regardless of rotation of the y-axis, is alternating between bright and dark.
After some trial and error i found out that i can get the correct shading by changing this
vec3 normal_viewspace = normal_matrix * normalize((normal_color.xyz * 2.0) - 1.0);
to this
vec3 normal_viewspace = normal_matrix * normalize(vec3(0.0, 0.0, 1.0));
Diffuse and specular lighting are now working correctly,
but obviously without the normal map applied. I honestly have no idea where exactly the error is originating. I am quite new to shader programming and was following this tutorial. Below are the shader sources, with all irrelevant parts cut.
Vertex shader:
#version 450
layout(location = 0) in vec3 position;
layout(location = 1) in vec3 normal;
layout(location = 2) in vec3 tangent;
layout(location = 3) in vec3 bitangent;
layout(location = 4) in vec2 texture_coordinates;
layout(location = 0) out mat3 normal_matrix;
layout(location = 3) out vec2 texture_coordinates_out;
layout(location = 4) out vec4 vertex_position_viewspace;
layout(set = 0, binding = 0) uniform Matrices {
mat4 world;
mat4 view;
mat4 projection;
} uniforms;
void main() {
mat4 worldview = uniforms.view * uniforms.world;
normal_matrix = mat3(worldview) * mat3(normalize(tangent), normalize(bitangent), normalize(normal));
vec4 vertex_position_worldspace = uniforms.world * vec4(position, 1.0);
vertex_position_viewspace = uniforms.view * vertex_position_worldspace;
gl_Position = uniforms.projection * vertex_position_viewspace;
texture_coordinates_out = texture_coordinates;
}
Fragment shader:
#version 450
layout(location = 0) in mat3 normal_matrix;
layout(location = 3) in vec2 texture_coordinates;
layout(location = 4) in vec4 vertex_position_viewspace;
layout(location = 0) out vec4 fragment_color;
layout(set = 0, binding = 0) uniform Matrices {
mat4 world;
mat4 view;
mat4 projection;
} uniforms;
// ...
layout (set = 0, binding = 2) uniform sampler2D normal_map;
// ...
const vec4 LIGHT = vec4(1.25, 3.0, 3.0, 1.0);
void main() {
// ...
vec4 normal_color = texture(normal_map, texture_coordinates);
// ...
vec3 normal_viewspace = normal_matrix * normalize((normal_color.xyz * 2.0) - 1.0);
vec4 light_position_viewspace = uniforms.view * LIGHT;
vec3 light_direction_viewspace = normalize((light_position_viewspace - vertex_position_viewspace).xyz);
vec3 view_direction_viewspace = normalize(vertex_position_viewspace.xyz);
vec3 light_color_intensity = vec3(1.0, 1.0, 1.0) * 7.0;
float distance_from_light = distance(vertex_position_viewspace, light_position_viewspace);
float diffuse_strength = clamp(dot(normal_viewspace, light_direction_viewspace), 0.0, 1.0);
vec3 diffuse_light = (light_color_intensity * diffuse_strength) / (distance_from_light * distance_from_light);
// ...
fragment_color.rgb = (diffuse_color.rgb * diffuse_light);
fragment_color.a = diffuse_color.a;
}
There are some things i am a bit uncertain about. For example i noticed that in the tutorial, the light is called lightPosition_worldSpace, making me think i need to multiply the light by the world matrix first, but doing so only makes my light rotate with the cube and still doesn't fix my lighting issue.
Any help or ideas on what i could be doing wrong would be greatly appreciated.
I'm the one who created the tutorial site you're referencing.
If possible could you share a link to your normal map as well? When you say that when you changed the line where the normal of the fragment is calculated using the normal map from this
vec3 normal_viewspace = normal_matrix * normalize((normal_color.xyz * 2.0) - 1.0);
to one where you hardcode a value like this
vec3 normal_viewspace = normal_matrix * normalize(vec3(0.0, 0.0, 1.0));
and that fixes the rendering issue, it seems to indicate an issue with the normal map itself.
One way to verify this is to set your entire normal map image to the RGB value (128, 128, 255), which is exactly the same as the vec3(0.0, 0.0, 1.0) value you were using in your changed line. If this results in the object rendering correctly the same as when you were using a hardcoded value, that means you were using a bad normal map.
The normal map is just a texture/image that stores the directions of the normals of your object in "tangent-space" (think of it as like if you had to flatten out your entire object into a 2D surface, and then the normals for each point of that surface is plotted on the map). For each pixel, the red channel represents the X-axis, the green channel represents the Y-axis, and the blue channel represents the Z-axis.
With colors, the range of colors in a normal map goes from (0, 0, 128) to (255, 255, 255) (for images where each color channel uses 8 bits/1 byte), but in GLSL this would be a range from (0.0, 0.0, 0.5) to (1.0, 1.0, 1.0). Let's just work with the range that is used in GLSL for the sake of simplicity.
When looking at the actual possible values for normals, their range actually is (-1.0, -1.0, 0.0) to (1.0, 1.0, 1.0) because you can have a normal direction be either forwards or backwards in either the X-axis or Y-axis.
So when we have a color value of (0.0, 0.0, 0.5), we're actually talking about a normal direction vector (-1.0, -1.0, 0.0). Similarly, a color value of (0.5, 0.5, 0.5) means the normal direction vector (0.0, 0.0, 0.0), and a color value of (1.0, 1.0, 1.0) means a normal value of (1.0, 1.0, 1.0).
So the goal now becomes transforming the value from the normal map from the color value range ((0.0, 0.0, 0.5) to (1.0, 1.0, 1.0)) to the actual range for normals ((-1.0, -1.0, 0.0) to (1.0, 1.0, 1.0)).
If you multiply a value from a normal map by 2.0, you change the possible range of the value from (0.0, 0.0, 0.5) - (1.0, 1.0, 1.0) to (0.0, 0.0, 1.0) - (2.0, 2.0, 2.0). And then if you subtract 1.0 from the result, the range now changes from (0.0, 0.0, 1.0) - (2.0, 2.0, 2.0) to (-1.0, -1.0, 0.0) - (1.0, 1.0, 1.0), which is exactly the possible range of the normals of an object.
So you have to make sure that when you're creating your normal map, the range of the RGB color values is between (0, 0, 128) - (255, 255, 255).
Side note: As for why the range of the blue channel (Z-axis) in the normal map can only be between 128 to 255, a value less than 128 means that a negative value on the Z-axis, meaning that the normal of the fragment is pointing into the surface, not out of it. Since a normal map is supposed to represent the values of the normals when the surface of the object is flattened and facing towards you, having a normal with a negative Z-axis value would mean that at that point the surface is actually facing away from you, which doesn't really make sense, hence why negative values are not allowed.
You could still try having the blue channel be a value less than 128 and see what interesting results pop out.
Also with regards to the doubt you mentioned in the end and in the comments:
What does lightPosition_worldSpace mean?
lightPosition_worldSpace represents the coordinate at which light is present relative to the center of the world (relative to the entire world you're rendering), hence the world-space suffix. You just need to multiply this position with the your view-matrix if you wish to know the position of the light is view-space (relative to your camera).
If you have a coordinate that is relative to the center of the object you're rendering, then you should multiply it with your model matrix (uniforms.world) to transform that coordinate from one that's relative to the center of your model to one that's relative to the center of the world. Since the lightPosition_worldSpace is the position of the light already relative to the center of the world, you don't need to multiply them. This is why you saw the behavior of the light moving with the cube when you did try to do so (the light was moved since its coordinates were thought to be placed relative to the cube itself).
Your comment regarding confusion with the line vec3 view_direction_viewspace = normalize(vertex_position_viewspace.xyz - vec3(0.0, 0.0, 0.0));
This is bad on my part for not representing what vec3(0.0, 0.0, 0.0) is with a variable. This is supposed to represent the position of the camera in view-space. Since in view-space the camera is at the center, its coordinate is vec3(0.0, 0.0, 0.0).
As for why I'm doing
vec3 view_direction_viewspace = normalize(vertex_position_viewspace.xyz - vec3(0.0, 0.0, 0.0));
when
vec3 view_direction_viewspace = normalize(vertex_position_viewspace.xyz);
is simpler and is basically the same thing, I had written it so to make it more obvious what was happening (which it appears I failed to do).
Typically, when you have two coordinates and you want to find the direction from a source coordinate to a destination coordinate you subtract the two coordinates to get their direction + magnitude. By normalizing that difference, you then just the directional component, with the magnitude part removed. So the equation for finding a direction from a source coordinate to a destination coordinate becomes:
direction = normalize(destination coordinate - source coordinate)
view_direction_viewspace Is supposed to represent the direction from the camera towards the fragment. To calculate this, we can just subtract the position of the camera (vec3(0.0, 0.0, 0.0)) from the position of the fragment (vertex_position_viewspace.xyz) and then run normalize(...) on the difference to get that result.
I've generally tried to maintain this consistency where when I'm calculating a direction using two coordinates I always have a destination and source coordinate explicitly written out, hence why you see the line vec3 view_direction_viewspace = normalize(vertex_position_viewspace.xyz - vec3(0.0, 0.0, 0.0)); in the fragment shader code.
I've updated the code by setting vec3(0.0, 0.0, 0.0) to a variable cameraPosition_viewSpace and using that to better clarify this intention.
Feel free to reach out through GitHub issues if you want to ask anything else or help improve the tutorial.
I haven't updated this post in a while because i have completely shifted away from using normal mapping (for now) but still wanted to post an answer, in case that someone else runs into the same problem. I still can't be 100% sure but i am fairly certain, that this behavior was caused by the library i was using to load the normal map. Special thanks to sabarnac who has been a huge help to me in solving this.
I’m reading OpenGL Programming Guide, Ninth Edition.
I’m in trouble with this:
#version 420 core
uniform mat4 model_matrix;
…
layout (location = 0) in vec4 position;
…
void main(void)
{
vec4 pos = (model_matrix * (position * vec4(1.0, 1.0, 1.0, 1.0)));
…
};
So, what’s the point in multiplying "position" times vec4(1.0, 1.0, 1.0, 1.0)? The result will be "position" with or without vec4(1.0, 1.0, 1.0, 1.0).
I checked it in the Red book and there is no specific reason there, then it is just about a scale to the vertices positions in case that vector is different of Vector4.One and you want to do a scale, but if it is just a units vector, there is no need to do it and you can simple remove the redundancy.
So, I'm trying to rotate a light around a stationary object in the center of my scene. I'm well aware that I will need to use the rotation matrix in order to make this transformation occur. However, I'm unsure of how to do it in code. I'm new to linear algebra, so any help with explanations along the way would help a lot.
Basically, I'm working with these two right now and I'm not sure of how to make the light circulate the object.
mat4 rotation = mat4(
vec4( cos(aTimer), 0.0, sin(aTimer), 0.0),
vec4( 0, 1.0, 0.0, 0.0),
vec4(-sin(aTimer), 0.0, cos(aTimer), 0.0),
vec4( 0.0, 0.0, 0.0, 1.0)
);
and this is how my light is set up :
float lightPosition[4] = {5.0, 5.0, 1.0, 0};
glLightfv(GL_LIGHT0, GL_POSITION, lightPositon);
The aTimer in this code is a constantly incrementing float.
Even though you want the light to rotate around your object, you must not use a rotation matrix for this purpose but a translation one.
The matrix you're handling is the model matrix. It defines the orientation, the position and the scale of your object.
The matrix you have here is a rotation matrix, so the orientation of the light will change, but not the position, which is what you want.
So there is two problems to fix here :
1.Define your matrix properly. Since you want a translation (circular), I think this is the matrix you need :
mat4 rotation = mat4(
vec4( 1.0, 0.0, 0.0, 0.0),
vec4( 0.0, 1.0, 0.0, 0.0),
vec4( 0.0, 0.0, 1.0, 0.0),
vec4( cos(aTimer), sin(aTimer), 0.0, 1.0)
);
2.Define a good position vertex for your light. Since it's a single vertex and it's the job of the model matrix (above) to move the light, the light vector 4D should be :
float lightPosition[4] = {0.0f, 0.0f, 0.0f, 1.0f};
//In C, 0.0 is a double, you may have warnings at compilation for loss of precision, so use the suffix "f"
The forth component must be one since it's thanks to it that translations are possible.
You may find additional information here
Model matrix in 3D graphics / OpenGL
However they are using column vectors. Judging from your rotation matrix I do belive you use row vectors, so the translation components are in the last row, not the last column of the model matrix.
I have created this simple fragment shader for achieving a vertical color gradient effect.
But I find this to be taxing for my mobile device in full screen.
is there any way to optimize this?
here is the link to the code
http://glsl.heroku.com/e#13541.0
You could do something like this instead.
vec2 position = (gl_FragCoord.xy / resolution.xy);
vec4 top = vec4(1.0, 0.0, 1.0, 1.0);
vec4 bottom = vec4(1.0, 1.0, 0.0, 1.0);
gl_FragColor = vec4(mix(bottom, top, position.y));
Example
You can further change the color yourself, I just used random colors.
You can even further eliminate calculating the x but that's kinda overkill.
vec4 top = vec4(1.0, 0.0, 1.0, 1.0);
vec4 bottom = vec4(1.0, 1.0, 0.0, 1.0);
gl_FragColor = vec4(mix(bottom, top, (gl_FragCoord.y / resolution.y)));
...and have it actually work. I get the principle, you write a vertex program, something like, this say:
attribute vec3 v_pos;
attribute vec4 v_color;
attribute vec2 v_uv;
attribute vec3 v_rotation; // [angle, x, y]
uniform mat4 modelview_mat;
uniform mat4 projection_mat;
varying vec4 frag_color;
varying vec2 uv_vec;
void main (void) {
mat4 trans_in = mat4(
1.0, 0.0, 0.0, 50.0, // <--- Transformation matrix
0.0, 1.0, 0.0, 50.0,
0.0, 0.0, 1.0, 50.0,
0.0, 0.0, 0.0, 1.0
);
vec4 pos = trans_in * vec4(v_pos,1.0); // <--- apply to input
// Mark a vertex using color to prove a transformation is actually happening...
if (v_rotation[0] > 10.0) {
frag_color = vec4(1.0, 0.0, 0.0, 1.0);
gl_Position = projection_mat * vec4(pos[0], pos[1], 1.0, 1.0);
}
// And leave all the other verticies untouched.
else {
frag_color = v_color;
gl_Position = projection_mat * vec4(v_pos, 1.0); // <--- Untransformed output
}
uv_vec = v_uv; // <--- Pass UV to fragment program
}
The problem is, this doesn't actually work.
After applying the matrix transformation trans_in * v_pos, I expect a point [1, 2, 3] to become [51, 52, 53, 1].
...but it doesn't. In fact, it renders this:
(ie. no transformation of the point location; pos = trans_in * v_pos == vec4(v_pos, 1.0)!!!!!! O_o)
Notice the red marked vertices that prove that I am actually setting the gl_Position for them; indeed, if I do this:
gl_Position = projection_mat * vec4(1.0, 1.0, 1.0, 1.0);
Each of those red points is jumped down to the bottom corner, as you would expect.
I've also tried various 3x3 matrix multiplications and it seems that while the scale operations work, and to some extent, the rotation operations work, I cannot for the life of me get any 2d translation operations to run; the matrix multiplication just seems to... do nothing.
What am I doing wrong?
You got the matrix order wrong. GLSL uses column-major oder, so each row in your intializer will become a column of the matrix. This refelcts the same convention which was used with the (now deprecated) GL matrix stack. It is also consistent to the setting of the transpose parameter of glUinformMatrix*() calls which has to be set to GL_FALSE for column major input (where translation part are elements m[12],m[13],m[14] in an 1D array).
Your matrix actually only alters the w component of your vector, which you then ignore, so it does not have any visible effect.