Previously we multiplied the interpolated texture coordinates by
width - 1 and height - 1 instead of width and height which resulted in
some wrongly mapped textures, especially visible in the glquake light
maps.
This also corrects the wrap mode being wrongly swapped for s/t
coordinates.
Since we do not have texture borders implemented yet we always use
GL_CLAMP_TO_EDGE for all clamping wrap modes for the time being.
If an unsupported drawing mode was configured, `glEnd` would not reach
the line where `m_in_draw_state` was set to `false`. This caused all
subsequent invocations to `glBegin` to fail.
Most resources seem to suggest that points on the clip planes are also
inside the frustum, e.g.: https://www.cubic.org/docs/3dclip.htm
This seems to resolve some rendering issues in Grim Fandango in OpenGL
mode where the screen remained black. This was because of quads being
drawn with their vertex positions exactly on the clip planes.
In its current state, ScummVM seems to invoke these methods just after
destroying the current GL context. According to the OpenGL spec:
"Issuing GL commands when the program does not have a current
context results in undefined behavior, up to and including program
termination."
Our old behavior was to deref a `nullptr`, which isn't that great. For
now, protect these two methods. If other ports seem to misbehave as
well, we can always expand the check to other methods.
The `glGet*` family of functions requires that all parameters of
different types are transparently converted into each other. For
example, you can request a boolean parameter as a float or a list of
double values as an integer. It might be considered bad practice to
request parameters through the wrongly-typed function, but to be spec-
compliant we need to implement this.
Introduce a new `::get_context_parameter()` to obtain a parameter
value, which is then converted to the right type by the respective
`::gl_get_*()` functions.
GLES 2.0 is a subset of OpenGL, so we allow applications to compile
against LibGL as if it fully supports GLES 2.0.
Additionally, we set the definitions to an integer value of `1` so
applications that check for availability like this...
int main() { return GL_ES_VERSION_2_0; }
...can actually compile. At least ScummVM uses this, and Mesa defines
their constants in the same way:
44b9e11ddb/include/GL/gl.h (L105)
As stated in the manual:
glDeleteTextures silently ignores 0's and names that do not
correspond to existing textures.
If we do not skip these 0 names, they end up as invalid free texture
names in our name allocator.
These enums are used to indicate byte-alignment when reading from and
to textures. The `GL_UNPACK_ROW_LENGTH` value was reimplemented to
support overriding the source data row width.
