android.renderscript

This class gives users a simple way to draw hardware accelerated text. Internally, the glyphs are rendered using the Freetype library and an internal cache of rendered glyph bitmaps is maintained. Each font object represents a combination of a typeface, and point size. You can create multiple font objects to represent styles such as bold or italic text, faces, and different font sizes. During creation, the Android system quieries device's screen DPI to ensure proper sizing across multiple device configurations.

Fonts are rendered using screen-space positions and no state setup beyond binding a font to the Renderscript is required. A note of caution on performance, though the state changes are transparent to the user, they do happen internally, and it is more efficient to render large batches of text in sequence. It is also more efficient to render multiple characters at once instead of one by one to improve draw call batching.

Font color and transparency are not part of the font object and you can freely modify them in the script to suit the user's rendering needs. Font colors work as a state machine. Every new call to draw text uses the last color set in the script.

This class is a container for geometric data displayed with Renderscript. Internally, a mesh is a collection of allocations that represent vertex data (positions, normals, texture coordinates) and index data such as triangles and lines.

Vertex data could either be interleaved within one allocation that is provided separately, as multiple allocation objects, or done as a combination of both. When a vertex channel name matches an input in the vertex program, Renderscript automatically connects the two together.

Parts of the mesh can be rendered with either explicit index sets or primitive types.

The Renderscript fragment program, also known as fragment shader is responsible for manipulating pixel data in a user defined way. It's constructed from a GLSL shader string containing the program body, textures inputs, and a Type object that describes the constants used by the program. Similar to the vertex programs, when an allocation with constant input values is bound to the shader, its values are sent to the graphics program automatically.

The values inside the allocation are not explicitly tracked. If they change between two draw calls using the same program object, the runtime needs to be notified of that change by calling rsgAllocationSyncAll so it could send the new values to hardware. Communication between the vertex and fragment programs is handled internally in the GLSL code. For example, if the fragment program is expecting a varying input called varTex0, the GLSL code inside the program vertex must provide it.

ProgramFragmentFixedFunction is a helper class that provides a way to make a simple fragment shader without writing any GLSL code. This class allows for display of constant color, interpolated color from the vertex shader, or combinations of the both blended with results of up to two texture lookups.