QShaderProgram Class

Detailed Description

A shader program consists of several different shaders, such as vertex and fragment shaders.

Qt3D will automatically populate a set of default uniforms if they are encountered during the shader instrospection phase.

RHI Support

When writing GLSL 450 shader code to use with Qt 3D's RHI backend, the default uniforms will be provided as 2 uniform buffer objects.

The binding locations for these is set to bindings 0 for RenderView uniforms and 1 for Command uniforms.

 #version 450 core

 layout(location = 0) in vec3 vertexPosition;

 layout(std140, binding = 0) uniform qt3d_render_view_uniforms {
   mat4 viewMatrix;
   mat4 projectionMatrix;
   mat4 uncorrectedProjectionMatrix;
   mat4 clipCorrectionMatrix;
   mat4 viewProjectionMatrix;
   mat4 inverseViewMatrix;
   mat4 inverseProjectionMatrix;
   mat4 inverseViewProjectionMatrix;
   mat4 viewportMatrix;
   mat4 inverseViewportMatrix;
   vec4 textureTransformMatrix;
   vec3 eyePosition;
   float aspectRatio;
   float gamma;
   float exposure;
   float time;
   float yUpInNDC;
   float yUpInFBO;
 };

 layout(std140, binding = 1) uniform qt3d_command_uniforms {
   mat4 modelMatrix;
   mat4 inverseModelMatrix;
   mat4 modelViewMatrix;
   mat3 modelNormalMatrix;
   mat4 inverseModelViewMatrix;
   mat4 modelViewProjection;
   mat4 inverseModelViewProjectionMatrix;
 };

 void main()
 {
     gl_Position = (projectionMatrix * viewMatrix * modelMatrix * vertexPosition);
 }

For user defined uniform buffer object, use binding starting at 2 or auto to let Qt 3D work out the binding automatically. Make sure to remain consistent between the different shader stages.

 #version 450 core

 layout(std140, binding = auto) uniform my_uniforms {
   vec4 myColor;
 };

 layout(location=0) out vec4 fragColor;

 void main()
 {
     fragColor = myColor;
 }

There is no change involved when it comes to feeding values to uniforms.

For the above example, setting myColor could be done with:

 QParameter *parameter = new QParameter();
 parameter->setName("myColor");
 parameter->setValue(QVariant::fromValue(QColor(Qt::blue)));

Textures still have to be defined as standalone uniforms.

 #version 450 core

 layout(binding=0) uniform sampler2D source;

 layout(location=0) out vec4 fragColor;

 void main()
 {
     fragColor = texture(source, vec2(0.5, 0.5));
 }