I'm currently porting Oculus Rift's shaders to GLSL 330, but I'm getting strange errors:

ERROR: 0:36: error(#202) No matching overloaded function found: mix
ERROR: 0:36: error(#160) Cannot convert from: "const float" to: "highp 4X4 matrix of mat4"
ERROR: error(#273) 2 compilation errors. No code generated

At this line:

mat4 lerpedEyeRot = mix(u_EyeRotationStart, u_EyeRotationEnd, in_TimewarpLerpFactor);

I also tried to convert the last mix parameter to a mat4, with no luck

I'm using OpenGL 3.3 on Windows 7, my graphic card is an AMD Radeon HD 6670.

Here is the vertex shader at time of writing:

#version 330

layout (location = 0) in vec3 in_Position;
//layout (location = 1) in vec4 in_Color;
layout (location = 2) in vec2 in_TexCoord0; // R
layout (location = 3) in vec2 in_TexCoord1; // G
layout (location = 4) in vec2 in_TexCoord2; // B
layout (location = 5) in float in_Vignette;
layout (location = 6) in float in_TimewarpLerpFactor;

uniform vec2 u_EyeToSourceUVScale;
uniform vec2 u_EyeToSourceUVOffset;
uniform mat4 u_EyeRotationStart;
uniform mat4 u_EyeRotationEnd;

out float v_Vignette;
smooth out vec2 v_TexCoord0;
smooth out vec2 v_TexCoord1;
smooth out vec2 v_TexCoord2;

vec2 TimewarpTexCoord(vec2 TexCoord, mat4 rotMat)
{
	// Vertex inputs are in TanEyeAngle space for the R,G,B channels (i.e. after chromatic
	// aberration and distortion). These are now "real world" vectors in direction (x,y,1)
	// relative to the eye of the HMD. Apply the 3x3 timewarp rotation to these vectors.
	vec3 transformed = vec3( mul(rotMat, vec4(TexCoord.xy, 1.0, 1.0)).xyz);
	// Project them back onto the Z=1 plane of the rendered images.
	vec2 flattened = (transformed.xy / transformed.z);
	// Scale them into ([0,0.5],[0,1]) or ([0.5,0],[0,1]) UV lookup space (depending on eye)
	return u_EyeToSourceUVScale * flattened + u_EyeToSourceUVOffset;
}

void main()
{
	mat4 lerpedEyeRot = mix(u_EyeRotationStart, u_EyeRotationEnd, in_TimewarpLerpFactor); // ERROR HERE
	v_TexCoord0 = TimewarpTexCoord(in_TexCoord0, lerpedEyeRot);
	v_TexCoord1 = TimewarpTexCoord(in_TexCoord1, lerpedEyeRot);
	v_TexCoord2 = TimewarpTexCoord(in_TexCoord2, lerpedEyeRot);
	gl_Position = vec4(in_Position.xy, 0.5, 1.0);
	v_Vignette = in_Vignette; // For vignette fade
}

Looking at the docs, I don't think mix is defined for matrix interpolation at all. You might want to write up a custom function for it.

Looking at this doc, I thought it was supported...

Ok, so I wrote this instead:

mat4 lerpMatrix(mat4 a, mat4 b, float t)
{
	return a + (b - a) * t;
}

Not sure if it's the best method, but now the shader compiles.

Looking at this doc, I thought it was supported...