// Let's find a suitable pixel format -- first try with antialiasing
func BestwglChoosePixelFormatARB(procs *C.wglProcs, hdc C.HDC, bitsPerPixel uint, settings *ContextSettings) C.int {
if settings.AntialiasingLevel <= 0 {
return 0
}
if procs.p_wglChoosePixelFormatARB == nil {
return 0
}
AttribIList := [...]C.int{
C.WGL_DRAW_TO_WINDOW_ARB, C.GL_TRUE,
C.WGL_SUPPORT_OPENGL_ARB, C.GL_TRUE,
C.WGL_ACCELERATION_ARB, C.WGL_FULL_ACCELERATION_ARB,
C.WGL_DOUBLE_BUFFER_ARB, C.GL_TRUE,
C.WGL_SAMPLE_BUFFERS_ARB, C.GL_TRUE, // turn on antialiasing
C.WGL_SAMPLES_ARB, C.int(settings.AntialiasingLevel),
0, 0,
}
AttribFList := []C.FLOAT{0, 0}
// Let's check how many formats are supporting our requirements
const formats_size = 128
var formats [formats_size]C.int
var nbFormats C.UINT
for settings.AntialiasingLevel > 0 {
if C.__wglChoosePixelFormatARB(procs, hdc, &AttribIList[0], &AttribFList[0], formats_size, &formats[0], &nbFormats) == C.TRUE &&
nbFormats > 0 {
break
}
nbFormats = 0 // reset this
// Decrease the antialiasing level until we find a valid one
settings.AntialiasingLevel--
AttribIList[11]--
}
bestScore := uint(1<<32 - 1)
var bestFormat C.int
for i := C.UINT(0); bestScore != 0 && i < nbFormats; i++ {
// Get the current format's attributes
attributes := C.PIXELFORMATDESCRIPTOR{
nSize: C.PIXELFORMATDESCRIPTOR_size,
nVersion: 1,
}
if C.__DescribePixelFormat(hdc, formats[i], C.PIXELFORMATDESCRIPTOR_size, &attributes) == 0 {
return 0
}
// Evaluate the current configuration
color := uint(attributes.cRedBits + attributes.cGreenBits + attributes.cBlueBits + attributes.cAlphaBits)
score := EvaluateFormat(bitsPerPixel, *settings, color, uint(attributes.cDepthBits), uint(attributes.cStencilBits), settings.AntialiasingLevel)
// Keep it if it's better than the current best
if score < bestScore {
bestScore = score
bestFormat = formats[i]
}
}
return bestFormat
}
func createContext(procs *C.wglProcs, sharedContext C.HGLRC, hdc C.HDC, bitsPerPixel uint, settings *ContextSettings) C.HGLRC {
bestFormat := BestwglChoosePixelFormatARB(procs, hdc, bitsPerPixel, settings)
if bestFormat == 0 {
bestFormat = BestChoosePixelFormat(hdc, bitsPerPixel, settings)
}
if bestFormat == 0 {
return nil // Failed to find a suitable pixel format for device context -- cannot create OpenGL context
}
// Extract the depth and stencil bits from the chosen format
actualFormat := C.PIXELFORMATDESCRIPTOR{
nSize: C.PIXELFORMATDESCRIPTOR_size,
nVersion: 1,
}
if C.__DescribePixelFormat(hdc, bestFormat, C.PIXELFORMATDESCRIPTOR_size, &actualFormat) == 0 {
return nil
}
settings.DepthBits = uint(actualFormat.cDepthBits)
settings.StencilBits = uint(actualFormat.cStencilBits)
// Set the chosen pixel format
if C.SetPixelFormat(hdc, bestFormat, &actualFormat) == C.FALSE {
return nil // Failed to set pixel format for device context -- cannot create OpenGL context
}
if procs.p_wglCreateContextAttribsARB != nil {
for settings.MajorVersion >= 3 {
attributes := [...]C.int{
C.WGL_CONTEXT_MAJOR_VERSION_ARB, C.int(settings.MajorVersion),
C.WGL_CONTEXT_MINOR_VERSION_ARB, C.int(settings.MinorVersion),
C.WGL_CONTEXT_PROFILE_MASK_ARB, C.WGL_CONTEXT_COMPATIBILITY_PROFILE_BIT_ARB,
0, 0,
}
if context := C.__wglCreateContextAttribsARB(procs, hdc, sharedContext, &attributes[0]); context != nil {
return context
}
// If we couldn't create the context, lower the version number and try again -- stop at 3.0
// Invalid version numbers will be generated by this algorithm (like 3.9), but we really don't care
if settings.MinorVersion > 0 {
// If the minor version is not 0, we decrease it and try again
settings.MinorVersion--
} else {
// If the minor version is 0, we decrease the major version
settings.MajorVersion--
settings.MinorVersion = 9
}
}
}
// set the context version to 2.0 (arbitrary)
settings.MajorVersion = 2
settings.MinorVersion = 0
context := C.wglCreateContext(hdc)
if context == nil {
return nil // Failed to create an OpenGL context for this window
}
// Share this context with others
C.wglShareLists(sharedContext, context)
return context
}