.DrawFuelLevel STMFD R13!, {R10-R12, R14} \ Store the registers that we want to use on \ the stack so they can be preserved LDR R1, [R11, #fuelLevel] \ Set R1 to the current fuel level in \ fuelLevel LDRB R2, [R11, #fuelBurnRate] \ Set R2 to the current fuel burn rate in \ fuelBurnRate SUBS R1, R1, R2 \ Subtract the fuel burn rate from the fuel MOVMI R1, #0 \ level, making sure it doesn't fall below STR R1, [R11, #fuelLevel] \ zero, and store the updated fuel level in \ fuelLevel (and leaving the value in R1) LDR R7, screenAddr \ Set R7 to the address of the screen bank \ we are drawing in, pointing just below \ the two lines of text at the top of the \ screen ADD R11, R7, #320 \ Set R11 to the address in R7, plus 320 to \ move it down by one pixel line LDR R8, fuelBarColour \ Set R8 to the four-pixel colour word that \ we need to poke into screen memory to draw \ four pixels in the correct colour for the \ fuel bar MOV R10, R1, LSR #4 \ Set R10 = R1 >> 4 \ = fuel level / 16 BL DrawHorizontalLine \ Draw a horizontal line of length R10, \ starting at screen address R11 and drawing \ to the right in the colour in R8, so \ that's the top pixel row of the bar ADD R11, R7, #2*320 \ Set R11 to the address in R7, plus 640 to \ move it down by two pixel lines LDR R8, fuelBarColour \ Set R8 to the four-pixel colour word that \ we need to poke into screen memory to draw \ four pixels in the correct colour for the \ fuel bar MOV R10, R1, LSR #4 \ Set R10 = R1 >> 4 \ = fuel level / 16 BL DrawHorizontalLine \ Draw a horizontal line of length R10, \ starting at screen address R11 and drawing \ to the right in the colour in R8, so \ that's the middle pixel row of the bar ADD R11, R7, #3*320 \ Set R11 to the address in R7, plus 960 to \ move it down by two pixel lines LDR R8, fuelBarColour \ Set R8 to the four-pixel colour word that \ we need to poke into screen memory to draw \ four pixels in the correct colour for the \ fuel bar MOV R10, R1, LSR #4 \ Set R10 = R1 >> 4 \ = fuel level / 16 BL DrawHorizontalLine \ Draw a horizontal line of length R10, \ starting at screen address R11 and drawing \ to the right in the colour in R8, so \ that's the bottom pixel row of the bar LDMFD R13!, {R10-R12, PC} \ Retrieve the registers that we stored on \ the stack and return from the subroutineName: DrawFuelLevel [Show more] Type: Subroutine Category: Score bar Summary: Draw the bar at the top of the screen showing the current fuel levelContext: See this subroutine in context in the source code References: This subroutine is called as follows: * MainLoop calls DrawFuelLevel
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Subroutine DrawHorizontalLine (category: Drawing lines)
Draw a horizontal line
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Variable fuelBarColour (category: Score bar)
A four-pixel colour word for the colour of the fuel bar
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Configuration variable fuelBurnRate = &15C
The current fuel burn rate (bit 0 is ignored)
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Configuration variable fuelLevel = &128
The player's fuel level
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Variable screenAddr (category: Drawing the screen)
The screen address for the start of the 17th pixel line in the current bank (i.e. the line just below the two rows of text)