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Cannot get uniform location from GLSL shader

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Hey there, I've got a little problem here with my shaders. I have two shaders, the first one populates a FBO with three textures: the color, the depth and the normal data. Now, the second shader should get these textures as parameters, but I cannot get the uniform location - it just return -1 when I try to get it. The first shader works nicely and I can use the textures after the draw calls are done, but I can't get the second shader to work. It does compile nicely, and no errors are raised.

Here's my "geometry pass":

// Load the shader and set the camera matrices
GL.UniformMatrix4(GL.GetUniformLocation(geometryShaderId, "view"), false, ref Engine.cameras[0].modelview);
GL.UniformMatrix4(GL.GetUniformLocation(geometryShaderId, "projection"), false, ref Engine.cameras[0].projection);

// Bind the frame buffer
GL.BindFramebuffer(FramebufferTarget.DrawFramebuffer, fboId);

// Enable depth stuff

// Clear
GL.ClearColor(0f, 0f, 0f, 1f);
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

// Render the geometry

// Clean up the geometry pass
GL.BindFramebuffer(FramebufferTarget.FramebufferExt, 0);

And here's the "lighting" pass, or, the part that actually bugs:

GL.BindFramebuffer(FramebufferTarget.FramebufferExt, fboId);

// Set the textures for the fragment shader
GL.Uniform1(GL.GetUniformLocation(pointLightShaderId, "colorMap"), 0); // <-- Location is -1
GL.BindTexture(TextureTarget.Texture2D, gbuffer.DiffuseTexture);

The lighting shader is initialized like this:

// Load shader files
string vText = File.ReadAllText("Resources/Shaders/pointlight_vertex.glsl");
string fText = File.ReadAllText("Resources/Shaders/pointlight_fragment.glsl");

// Create shader IDs
vertexId = GL.CreateShader(ShaderType.VertexShader);
fragmentId = GL.CreateShader(ShaderType.FragmentShader);

// Set shader sources
GL.ShaderSource(vertexId, vText);
GL.ShaderSource(fragmentId, fText);

// Compile vertex shader
string vertexLog = GL.GetShaderInfoLog(vertexId);
int vertexStatusCode;
GL.GetShader (vertexId, ShaderParameter.CompileStatus, out vertexStatusCode);
if(vertexStatusCode != 1) Console.WriteLine("Error creating vertex shader: " + vertexLog);

// Compile fragment shader
string fragmentLog = GL.GetShaderInfoLog(fragmentId);
int fragmentStatusCode;
GL.GetShader(fragmentId, ShaderParameter.CompileStatus, out fragmentStatusCode);
if(fragmentStatusCode != 1) Console.WriteLine("Error creating fragment shader: " + fragmentLog);

// Create the shader program
shaderId = GL.CreateProgram();
GL.AttachShader(shaderId, vertexId);
GL.AttachShader(shaderId, fragmentId);

GL.BindAttribLocation(shaderId, 0, "in_position");
GL.BindFragDataLocation(shaderId, 0, "out_light");


int programStatusCode;
GL.GetProgram(shaderId, ProgramParameter.ValidateStatus, out programStatusCode);
if(programStatusCode == (int)All.False)
Console.WriteLine("Error creating shader program!");


... And finally, here's the lighting shaders (stubs for now). Here's the vertex shader:

#version 330

uniform mat4 projection;
uniform mat4 view;
uniform mat4 world;

layout(location = 0) in vec3 in_position;

out vec3 worldpos;
out vec4 screenpos;

void main(void)
gl_Position = projection * view * world * vec4(0.0, 0.0, 0.0, 1.0);
worldpos = gl_Position.xyz;
screenpos = vec4(worldpos, 1.0);

... and here's the fragment shader:

#version 330

uniform sampler2D colorMap;

in vec3 worldpos;
in vec4 screenpos;
out vec4 out_light;

void main(void)
// Just try to paint with magenta, though it doesn't happen :(
out_light = vec4(1.0, 0.0, 1.0, 1.0);

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